{
  "body_content_embedded": false,
  "concept_count": 701,
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    {
      "concept_id": "r012:concept:absolute-convergence",
      "definition": "Convergence of a series after replacing every term by its absolute value.",
      "prerequisite_concept_ids": [
        "r012:concept:infinite-series"
      ],
      "source_label": "absolute convergence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_infinite-outcomes"
      ]
    },
    {
      "concept_id": "r012:concept:absorbing-markov-chain",
      "definition": "A Markov chain with an absorbing state reachable from every nonabsorbing state.",
      "prerequisite_concept_ids": [
        "r012:concept:absorbing-state"
      ],
      "source_label": "absorbing Markov chain",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_markov-chains"
      ]
    },
    {
      "concept_id": "r012:concept:absorbing-state",
      "definition": "A state whose self-transition probability is one and whose other outgoing probabilities are zero.",
      "prerequisite_concept_ids": [
        "r012:concept:markov-chain"
      ],
      "source_label": "absorbing state",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_markov-chains"
      ]
    },
    {
      "concept_id": "r012:concept:acyclic-graph",
      "definition": "A graph containing no cycle.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:cycle"
      ],
      "source_label": "acyclic graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro"
      ]
    },
    {
      "concept_id": "r012:concept:adaptive-wagering-without-replacement",
      "definition": "A wagering strategy that uses revealed pairings while sampling without replacement.",
      "prerequisite_concept_ids": [
        "r012:concept:conditional-probability",
        "r012:concept:sampling-without-replacement"
      ],
      "source_label": "adaptive wagering without replacement",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:07a5e2769ec7b1889ef21fcf"
      ]
    },
    {
      "concept_id": "r012:concept:addition-laws",
      "definition": "Associativity, commutativity, zero-sum, and cancellation properties derived from recursive addition.",
      "prerequisite_concept_ids": [
        "r012:concept:recursive-addition"
      ],
      "source_label": "laws of addition",
      "status": "source_frozen",
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        "r012:unit:s_background_add",
        "r012:unit:lem_sum0",
        "r012:unit:s_background_formal-num-sys"
      ]
    },
    {
      "concept_id": "r012:concept:addition-monotonicity",
      "definition": "Adding the same nonnegative integer preserves weak and strict inequalities.",
      "prerequisite_concept_ids": [
        "r012:concept:natural-number-order",
        "r012:concept:integer-addition"
      ],
      "source_label": "monotonicity of addition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_total-order-N"
      ]
    },
    {
      "concept_id": "r012:concept:additive-inverse",
      "definition": "For an integer x, the integer -x whose sum with x is zero.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-addition",
        "r012:concept:integer-zero"
      ],
      "source_label": "additive inverse",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_prop-integers"
      ]
    },
    {
      "concept_id": "r012:concept:adjacency",
      "definition": "Two vertices are adjacent when their pair is an edge.",
      "prerequisite_concept_ids": [
        "r012:concept:edge"
      ],
      "source_label": "adjacent vertices",
      "status": "source_frozen",
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        "r012:unit:s_intro_graph"
      ]
    },
    {
      "concept_id": "r012:concept:advancement-operator",
      "definition": "The operator A on integer-indexed functions defined by Af(n)=f(n+1), with A^p f(n)=f(n+p) for positive integers p.",
      "prerequisite_concept_ids": [
        "r012:concept:function",
        "r012:concept:sequence"
      ],
      "source_label": "advancement operator",
      "status": "source_frozen",
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        "r012:unit:s_recurrence_adv-ops",
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        "r012:unit:auto:45c00a23c466b44177d15161",
        "r012:unit:ex_recurrence_adveq",
        "r012:unit:auto:03810a7758a5b5bb714c9db1",
        "r012:unit:s_recurrence_adv-ops_const-coeff",
        "r012:unit:s_recurrence_adv-ops_roots-factors",
        "r012:unit:s_recurrence_solving",
        "r012:unit:s_recurrence_solving_homogeneous",
        "r012:unit:s_recurrence_solving_nonhomogeneous",
        "r012:unit:rqs-recurrence_solving",
        "r012:unit:s_recurrence_rigorous_principal",
        "r012:unit:s_recurrence_rigorous_start",
        "r012:unit:s_recurrence_rigorous_general"
      ]
    },
    {
      "concept_id": "r012:concept:advancement-operator-equation",
      "definition": "A recurrence equation represented as p(A)f=g using a polynomial in the advancement operator.",
      "prerequisite_concept_ids": [
        "r012:concept:advancement-operator",
        "r012:concept:linear-recurrence-equation"
      ],
      "source_label": "advancement operator equation",
      "status": "source_frozen",
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        "r012:unit:ex_recurrence_adveq",
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        "r012:unit:eqn_advance",
        "r012:unit:s_recurrence_adv-ops_zero",
        "r012:unit:rqs-recurrence_adv-ops",
        "r012:unit:rq-recurrence_adv-ops_rewrite",
        "r012:unit:s_recurrence_solving",
        "r012:unit:ex_recurrence_deg2",
        "r012:unit:ex_recurrence_ternary-strings-no-20-solved",
        "r012:unit:ex_recurrence_deg2-repeated",
        "r012:unit:ex_recurrence_deg4-repeated",
        "r012:unit:s_recurrence_solving_nonhomogeneous",
        "r012:unit:rqs-recurrence_solving"
      ]
    },
    {
      "concept_id": "r012:concept:advancement-operator-exercise-synthesis",
      "definition": "Practice translating recurrences into advancement-operator equations and solving homogeneous and nonhomogeneous factorizations, including repeated roots.",
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        "r012:concept:advancement-operator"
      ],
      "source_label": "advancement operator exercise synthesis",
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        "r012:unit:auto:f10a68b8c3ec6f2b75b92e9a",
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        "r012:unit:auto:7ed09f79b0fb4d1b7de08cae",
        "r012:unit:auto:2cfed815ad84a270e98c40b4"
      ]
    },
    {
      "concept_id": "r012:concept:advancement-operator-polynomial",
      "definition": "A polynomial p(A)=c_0A^k+c_1A^(k-1)+...+c_k whose action packages a constant-coefficient linear recurrence equation.",
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        "r012:concept:advancement-operator",
        "r012:concept:linear-recurrence-equation"
      ],
      "source_label": "polynomial in the advancement operator",
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        "r012:unit:s_recurrence_adv-ops_const-coeff",
        "r012:unit:eqn_advance",
        "r012:unit:s_recurrence_adv-ops_roots-factors",
        "r012:unit:s_recurrence_adv-ops_zero",
        "r012:unit:rq-recurrence_adv-ops_rewrite",
        "r012:unit:eqn_recurrence_deg2",
        "r012:unit:eqn_recurrence_ternary",
        "r012:unit:ex_recurrence_deg2-repeated",
        "r012:unit:eqn_recurrence_deg4-repeated",
        "r012:unit:auto:4a09aa7241b0bf6a931d0955",
        "r012:unit:auto:2b9501b6517e77e868e24689",
        "r012:unit:ex_recurrence_lines-solved",
        "r012:unit:auto:025bf0a72a4db690049c74bf",
        "r012:unit:rq-recurrence_solving-solve-plus-deg-two",
        "r012:unit:thm_advance",
        "r012:unit:eqn_nonhomogeneous",
        "r012:unit:eqn_homogeneous",
        "r012:unit:eqn_distinct",
        "r012:unit:eqn_rr"
      ]
    },
    {
      "concept_id": "r012:concept:aircraft-crew-positioning",
      "definition": "Assigning aircraft and crews to locations in response to schedule disruption.",
      "prerequisite_concept_ids": [
        "r012:concept:industrial-optimization",
        "r012:concept:scheduling-irregularity"
      ],
      "source_label": "aircraft and crew positioning",
      "status": "source_frozen",
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        "r012:unit:ch_epilogue"
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    {
      "concept_id": "r012:concept:algebraic-number",
      "definition": "A real number that is a root of a nonzero polynomial with integer coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:polynomial"
      ],
      "source_label": "algebraic number",
      "status": "source_frozen",
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        "r012:unit:s_background_complex"
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    },
    {
      "concept_id": "r012:concept:algebraic-transcendental-number",
      "definition": "An algebraic real is a root of an integer-coefficient polynomial; otherwise it is transcendental.",
      "prerequisite_concept_ids": [
        "r012:concept:real-number-as-cut",
        "r012:concept:polynomial"
      ],
      "source_label": "algebraic and transcendental real numbers",
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    {
      "concept_id": "r012:concept:algorithm",
      "definition": "A finite procedure for carrying out a computation or construction.",
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      "source_label": "algorithm",
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      "concept_id": "r012:concept:algorithms-optimization",
      "definition": "Procedures for constructing, testing, or optimizing combinatorial structures.",
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        "r012:concept:discrete-structures"
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      "source_label": "algorithms and optimization",
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    },
    {
      "concept_id": "r012:concept:alphabet",
      "definition": "The set of symbols from which the characters of a string are drawn.",
      "prerequisite_concept_ids": [
        "r012:concept:string"
      ],
      "source_label": "alphabet",
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    {
      "concept_id": "r012:concept:alternative-variance-identity",
      "definition": "Variance also equals E(X^2)-E(X)^2.",
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        "r012:concept:variance"
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      "source_label": "alternative variance identity",
      "status": "source_frozen",
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        "r012:unit:prop_altvar"
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    },
    {
      "concept_id": "r012:concept:antichain-partition",
      "definition": "A partition of the ground set of a poset into antichains.",
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        "r012:concept:partition",
        "r012:concept:poset-antichain"
      ],
      "source_label": "antichain partition",
      "status": "source_frozen",
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        "r012:unit:thm_dualdilworth",
        "r012:unit:fig_height5"
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    },
    {
      "concept_id": "r012:concept:antisymmetric-relation",
      "definition": "A relation R is antisymmetric when xRy and yRx together imply x=y.",
      "prerequisite_concept_ids": [
        "r012:concept:binary-relation"
      ],
      "source_label": "antisymmetric binary relation",
      "status": "source_frozen",
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        "r012:unit:s_background_order"
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    },
    {
      "concept_id": "r012:concept:applied-combinatorics",
      "definition": "Combinatorial methods used to model and solve concrete mathematical or computational problems.",
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        "r012:concept:combinatorics"
      ],
      "source_label": "applied combinatorics",
      "status": "source_frozen",
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        "r012:unit:ch_intro",
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      ]
    },
    {
      "concept_id": "r012:concept:arithmetic-combinatorics",
      "definition": "The study of additive and arithmetic patterns in sets and sequences of integers, with connections to Ramsey theory, number theory, and analysis.",
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        "r012:concept:number-theory",
        "r012:concept:ramsey-property"
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      "source_label": "arithmetic combinatorics",
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        "r012:unit:s_kitchensink_arithmetic-combinatorics"
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    },
    {
      "concept_id": "r012:concept:arithmetic-progression",
      "definition": "A sequence with a constant nonzero difference between successive terms.",
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        "r012:concept:sequence"
      ],
      "source_label": "arithmetic progression",
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      ]
    },
    {
      "concept_id": "r012:concept:aromatic-hydrocarbon",
      "definition": "A hydrocarbon whose molecular structure contains an aromatic ring system.",
      "prerequisite_concept_ids": [],
      "source_label": "aromatic hydrocarbon",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:asymmetric-lovasz-local-lemma",
      "definition": "Event-specific x(E) bounds guarantee a positive probability that all bad events fail.",
      "prerequisite_concept_ids": [
        "r012:concept:dependency-neighborhood"
      ],
      "source_label": "asymmetric Lovász Local Lemma",
      "status": "source_frozen",
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        "r012:unit:lem_LLL",
        "r012:unit:s_kitchensink_lovasz-local"
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    {
      "concept_id": "r012:concept:asymptotic-order",
      "definition": "A growth-rate class that suppresses constant factors as the input tends to infinity.",
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      "source_label": "asymptotic order",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_applying-local-lemma"
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    },
    {
      "concept_id": "r012:concept:asymptotic-solution",
      "definition": "A description of limiting growth rather than an exact finite value.",
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        "r012:concept:big-o",
        "r012:concept:exact-solution"
      ],
      "source_label": "asymptotic solution",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_exact"
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    {
      "concept_id": "r012:concept:attendant-software",
      "definition": "Supporting software developed alongside a primary system.",
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        "r012:concept:operating-system"
      ],
      "source_label": "attendant software",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
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    {
      "concept_id": "r012:concept:augmenting-flow-update",
      "definition": "Increase flow by delta on forward edges and decrease it by delta on backward edges of an augmenting path.",
      "prerequisite_concept_ids": [
        "r012:concept:augmenting-path"
      ],
      "source_label": "augmenting-flow update",
      "status": "source_frozen",
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        "r012:unit:prop_networkflow_update",
        "r012:unit:exa_networkflow_delta"
      ]
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    {
      "concept_id": "r012:concept:augmenting-path",
      "definition": "A source-to-sink path whose forward edges have spare capacity and whose backward edges carry positive flow.",
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        "r012:concept:path",
        "r012:concept:spare-capacity",
        "r012:concept:network-flow"
      ],
      "source_label": "augmenting path",
      "status": "source_frozen",
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        "r012:unit:exa_networkflow_augpath",
        "r012:unit:s_flowapplications_bip-match"
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    },
    {
      "concept_id": "r012:concept:axiom-of-choice",
      "definition": "A choice set can select exactly one element from each member of a suitable family of nonempty sets.",
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        "r012:concept:zfc-set-theory"
      ],
      "source_label": "axiom of choice",
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    },
    {
      "concept_id": "r012:concept:axiom-of-extensionality",
      "definition": "Sets having exactly the same elements are equal.",
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        "r012:concept:zfc-set-theory"
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      "source_label": "axiom of extensionality",
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    },
    {
      "concept_id": "r012:concept:axiom-of-infinity",
      "definition": "There is a set containing the empty set and closed under the von Neumann successor y∪{y}.",
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        "r012:concept:zfc-set-theory",
        "r012:concept:successor-function"
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      "source_label": "axiom of infinity",
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    },
    {
      "concept_id": "r012:concept:back-matter",
      "definition": "The book-closing apparatus containing appendices, indexes, and production notes.",
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      "source_label": "back matter",
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      "unit_ids": [
        "r012:unit:backmatter"
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    },
    {
      "concept_id": "r012:concept:base",
      "definition": "The radix that determines the available digits and their positional place values.",
      "prerequisite_concept_ids": [
        "r012:concept:positional-base-notation"
      ],
      "source_label": "numeral-system base",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_decimal"
      ]
    },
    {
      "concept_id": "r012:concept:base-case",
      "definition": "The initial instance or instances established directly in an inductive proof.",
      "prerequisite_concept_ids": [
        "r012:concept:mathematical-induction"
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      "source_label": "base case",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_strong-induction"
      ]
    },
    {
      "concept_id": "r012:concept:bead",
      "definition": "A colored position-bearing object in a necklace enumeration problem.",
      "prerequisite_concept_ids": [
        "r012:concept:necklace"
      ],
      "source_label": "bead",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_enum",
        "r012:unit:fig_intro_necklace"
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    },
    {
      "concept_id": "r012:concept:bernoulli-count-variance",
      "definition": "For n Bernoulli trials with success probability p, the success-count variance is np(1-p).",
      "prerequisite_concept_ids": [
        "r012:concept:variance",
        "r012:concept:bernoulli-trials"
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      "source_label": "variance of a Bernoulli-trial success count",
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        "r012:unit:auto:4bd593cb3ed0759f3af2567d"
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    {
      "concept_id": "r012:concept:bernoulli-trials",
      "definition": "Repeated mutually independent two-outcome trials with constant success probability p.",
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        "r012:concept:independent-events",
        "r012:concept:probability-space"
      ],
      "source_label": "Bernoulli trials",
      "status": "source_frozen",
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        "r012:unit:s_probability_bernoulli-trials"
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    },
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      "concept_id": "r012:concept:big-o",
      "definition": "An eventual asymptotic upper bound up to a positive constant factor.",
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        "r012:concept:computational-complexity"
      ],
      "source_label": "Big O notation",
      "status": "source_frozen",
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        "r012:unit:s_genfunction_distributions"
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    {
      "concept_id": "r012:concept:bijection",
      "definition": "A one-to-one and onto function, equivalently a reversible correspondence between two sets.",
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        "r012:concept:function",
        "r012:concept:injection"
      ],
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        "r012:unit:s_background_finite-sets",
        "r012:unit:exe_sb"
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    },
    {
      "concept_id": "r012:concept:bijective-transformation",
      "definition": "A reversible correspondence that transfers a counting problem to an equinumerous family.",
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        "r012:concept:counting"
      ],
      "source_label": "invertible transformation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_strings_lattice-paths-binomial-thm_activity"
      ]
    },
    {
      "concept_id": "r012:concept:binary-operation",
      "definition": "A total function from X times X to X.",
      "prerequisite_concept_ids": [
        "r012:concept:function"
      ],
      "source_label": "binary operation",
      "status": "source_frozen",
      "unit_ids": [
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        "r012:unit:s_background_mult",
        "r012:unit:s_background_formal-num-sys"
      ]
    },
    {
      "concept_id": "r012:concept:binary-relation",
      "definition": "A subset of a Cartesian product X times Y.",
      "prerequisite_concept_ids": [
        "r012:concept:set-membership",
        "r012:concept:cartesian-product"
      ],
      "source_label": "binary relation",
      "status": "source_frozen",
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        "r012:unit:s_background_relations",
        "r012:unit:s_background_order"
      ]
    },
    {
      "concept_id": "r012:concept:binary-string",
      "definition": "A finite string over a two-symbol alphabet.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence"
      ],
      "source_label": "binary string",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_bernoulli-trials"
      ]
    },
    {
      "concept_id": "r012:concept:binomial-coefficient",
      "definition": "The number of k-element subsets of an n-element set.",
      "prerequisite_concept_ids": [
        "r012:concept:combination"
      ],
      "source_label": "binomial coefficient",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_strings_combinations",
        "r012:unit:prop_strings_binomraw",
        "r012:unit:prop_strings_symmetric",
        "r012:unit:s_induction_bincoeffs",
        "r012:unit:fig_pascal",
        "r012:unit:exa_inclusion-exclusion_int-solns",
        "r012:unit:auto:0ccd82df017d6432c7a435f0",
        "r012:unit:auto:0faa5a1d42e8503171d0a48a",
        "r012:unit:s_genfunction_gen-bin-thm",
        "r012:unit:auto:8f3500f97b0ab7c55c94505a",
        "r012:unit:thm_newton-binomial",
        "r012:unit:s_probmeth_graph-ramsey",
        "r012:unit:s_ramsey_estimatesize",
        "r012:unit:s_ramsey_probability"
      ]
    },
    {
      "concept_id": "r012:concept:binomial-count-probability",
      "definition": "The probability of exactly i successes in n Bernoulli trials is binomial(n,i)p^i(1-p)^(n-i).",
      "prerequisite_concept_ids": [
        "r012:concept:bernoulli-trials",
        "r012:concept:combination"
      ],
      "source_label": "binomial count probability",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:db94db2f7872e2d60d2c14d9",
        "r012:unit:auto:32044d97999cdcfffee7f5b3"
      ]
    },
    {
      "concept_id": "r012:concept:binomial-theorem",
      "definition": "The expansion of a nonnegative integer power of a binomial using binomial coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:binomial-coefficient"
      ],
      "source_label": "Binomial Theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_strings_binom-thm",
        "r012:unit:thm_binomial",
        "r012:unit:s_genfunction_gen-bin-thm",
        "r012:unit:thm_newton-binomial"
      ]
    },
    {
      "concept_id": "r012:concept:bipartite-graph",
      "definition": "A graph whose vertex set can be partitioned into two independent sets.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:independent-set"
      ],
      "source_label": "bipartite graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_graphs_bipartite",
        "r012:unit:fig_graphs_k33"
      ]
    },
    {
      "concept_id": "r012:concept:bipartite-matching",
      "definition": "A matching in a graph whose vertices are divided into two parts.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:optimization",
        "r012:concept:bipartite-graph"
      ],
      "source_label": "bipartite matching",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:ch_flowapplications",
        "r012:unit:s_flowapplications_bip-match"
      ]
    },
    {
      "concept_id": "r012:concept:bipartite-matching-flow-reduction",
      "definition": "Add a source and sink and unit-capacity directed edges so integral flows correspond exactly to bipartite matchings.",
      "prerequisite_concept_ids": [
        "r012:concept:maximum-bipartite-matching",
        "r012:concept:unit-capacity-integral-flow"
      ],
      "source_label": "bipartite matching to flow reduction",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_bip-match"
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    },
    {
      "concept_id": "r012:concept:blocking-pair",
      "definition": "An unmatched pair whose members each prefer the other over their current match.",
      "prerequisite_concept_ids": [
        "r012:concept:stable-matching"
      ],
      "source_label": "blocking pair",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_stable-match"
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    },
    {
      "concept_id": "r012:concept:body-font",
      "definition": "The typeface used for the main prose of a typeset edition.",
      "prerequisite_concept_ids": [],
      "source_label": "body font",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:backmatter"
      ]
    },
    {
      "concept_id": "r012:concept:book-index",
      "definition": "An automatically generated locator index for indexed topics in the book.",
      "prerequisite_concept_ids": [
        "r012:concept:back-matter"
      ],
      "source_label": "index",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:6f074d6a8fcb7cf736f5fdd2",
        "r012:unit:backmatter"
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    },
    {
      "concept_id": "r012:concept:breadth-first-label-scan",
      "definition": "The queue-like scan discipline that processes labeled vertices in their labeling order.",
      "prerequisite_concept_ids": [
        "r012:concept:ford-fulkerson-labeling-algorithm"
      ],
      "source_label": "first labeled, first scanned",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:alg_labeling"
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    },
    {
      "concept_id": "r012:concept:brooks-theorem",
      "definition": "A connected graph has chromatic number at most its maximum degree except that complete graphs and odd cycles require one additional color.",
      "prerequisite_concept_ids": [
        "r012:concept:chromatic-number",
        "r012:concept:maximum-degree",
        "r012:concept:complete-graph",
        "r012:concept:cycle"
      ],
      "source_label": "Brooks' theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_exercises"
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    },
    {
      "concept_id": "r012:concept:bubble-sort",
      "definition": "A comparison-sorting algorithm that repeatedly exchanges adjacent out-of-order elements.",
      "prerequisite_concept_ids": [
        "r012:concept:sorting"
      ],
      "source_label": "bubble sort",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_sorting"
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    },
    {
      "concept_id": "r012:concept:burnside-lemma",
      "definition": "The number of orbits equals the average number of objects fixed by group elements.",
      "prerequisite_concept_ids": [
        "r012:concept:group-action",
        "r012:concept:fixed-set",
        "r012:concept:stabilizer"
      ],
      "source_label": "Burnside's lemma",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_burnside"
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    },
    {
      "concept_id": "r012:concept:cantor-diagonal-nonsurjection",
      "definition": "A diagonal decimal construction produces a real omitted by every proposed enumeration.",
      "prerequisite_concept_ids": [
        "r012:concept:decimal-expansion",
        "r012:concept:surjection"
      ],
      "source_label": "decimal diagonal nonsurjection",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_complex"
      ]
    },
    {
      "concept_id": "r012:concept:cartesian-product",
      "definition": "The set of ordered pairs whose first and second coordinates come from specified factor sets.",
      "prerequisite_concept_ids": [
        "r012:concept:set",
        "r012:concept:ordered-pair"
      ],
      "source_label": "Cartesian product",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_products"
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    },
    {
      "concept_id": "r012:concept:cartesian-product-cardinality",
      "definition": "The cardinality of a finite Cartesian product is the product of the factor cardinalities.",
      "prerequisite_concept_ids": [
        "r012:concept:finite-cardinality"
      ],
      "source_label": "cardinality of a Cartesian product",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:prop_xy"
      ]
    },
    {
      "concept_id": "r012:concept:catalan-lattice-path-decomposition",
      "definition": "A decomposition of a diagonal-bounded lattice path into two smaller paths that yields a Catalan convolution recurrence.",
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        "r012:concept:catalan-number",
        "r012:concept:lattice-path",
        "r012:concept:rubot-catalan-recurrence"
      ],
      "source_label": "Catalan recurrence by lattice-path decomposition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:a58313acc3d83680ca48be27"
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    },
    {
      "concept_id": "r012:concept:catalan-number",
      "definition": "A member of the sequence counting diagonal-bounded lattice paths and many equivalent combinatorial families.",
      "prerequisite_concept_ids": [
        "r012:concept:lattice-path",
        "r012:concept:binomial-coefficient"
      ],
      "source_label": "Catalan number",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:exa_lattice-Catalan",
        "r012:unit:s_strings_lattice-paths-binomial-thm_activity"
      ]
    },
    {
      "concept_id": "r012:concept:cayley-formula",
      "definition": "The number of labeled trees on n vertices is n raised to the power n-2.",
      "prerequisite_concept_ids": [
        "r012:concept:labeled-tree",
        "r012:concept:prufer-code",
        "r012:concept:bijection"
      ],
      "source_label": "Cayley's Formula",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_cayley"
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    },
    {
      "concept_id": "r012:concept:central-binomial-convolution",
      "definition": "The coefficient identity obtained by squaring the central-binomial generating function.",
      "prerequisite_concept_ids": [
        "r012:concept:central-binomial-generating-function",
        "r012:concept:power-series-product"
      ],
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      "unit_ids": [
        "r012:unit:auto:77bb8e40ef7c0def33263edd"
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    },
    {
      "concept_id": "r012:concept:central-binomial-generating-function",
      "definition": "The generating-function identity (1-4x)^(-1/2)=sum from n=0 to infinity of binom(2n,n)x^n.",
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        "r012:concept:generalized-binomial-theorem",
        "r012:concept:negative-half-binomial-coefficient",
        "r012:concept:generating-function"
      ],
      "source_label": "generating function for central binomial coefficients",
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        "r012:unit:t_sqrt",
        "r012:unit:auto:79d958c3e26c2de12eddca3f"
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    },
    {
      "concept_id": "r012:concept:central-tendency",
      "definition": "The degree to which a random variable is concentrated near its expected value.",
      "prerequisite_concept_ids": [
        "r012:concept:random-variable",
        "r012:concept:expected-value"
      ],
      "source_label": "central tendency",
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      "unit_ids": [
        "r012:unit:auto:cb7ff5c803d045f07d0f6a7c"
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    },
    {
      "concept_id": "r012:concept:chain-partition",
      "definition": "A partition of the ground set of a poset into chains.",
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        "r012:concept:partition",
        "r012:concept:poset-chain",
        "r012:concept:poset"
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      "source_label": "chain partition",
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        "r012:unit:thm_dilworth",
        "r012:unit:fig_width7",
        "r012:unit:ch_flowapplications",
        "r012:unit:s_flowapplications_chain-partition"
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    },
    {
      "concept_id": "r012:concept:chain-rule",
      "definition": "The differentiation rule for a composition of functions.",
      "prerequisite_concept_ids": [
        "r012:concept:function"
      ],
      "source_label": "chain rule",
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      "unit_ids": [
        "r012:unit:auto:f4036c5496787d4bb754e7c7"
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    },
    {
      "concept_id": "r012:concept:character",
      "definition": "A symbol occupying one position in a string.",
      "prerequisite_concept_ids": [
        "r012:concept:alphabet",
        "r012:concept:string"
      ],
      "source_label": "character",
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        "r012:unit:s_strings_intro"
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    },
    {
      "concept_id": "r012:concept:chebyshev-inequality",
      "definition": "A distribution-free bound controlling deviations from the expected value in units of standard deviation.",
      "prerequisite_concept_ids": [
        "r012:concept:variance",
        "r012:concept:standard-deviation",
        "r012:concept:markov-inequality"
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      "source_label": "Chebyshev's inequality",
      "status": "source_frozen",
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        "r012:unit:thm_chebyshev"
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    },
    {
      "concept_id": "r012:concept:checkerboard",
      "definition": "A rectangular array of equal cells used as the region to be tiled in a combinatorial model.",
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        "r012:concept:geometry"
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      "source_label": "checkerboard",
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      "unit_ids": [
        "r012:unit:auto:a5fd615b1106d334b47d57d4"
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    {
      "concept_id": "r012:concept:chromatic-number",
      "definition": "The minimum number of colors in a proper coloring of a graph.",
      "prerequisite_concept_ids": [
        "r012:concept:proper-coloring"
      ],
      "source_label": "chromatic number",
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      "unit_ids": [
        "r012:unit:s_graphs_color",
        "r012:unit:fig_graphs_chi4",
        "r012:unit:thm_girth",
        "r012:unit:s_ramsey_exercises"
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    },
    {
      "concept_id": "r012:concept:circle-permutation-double-count",
      "definition": "Count incidences between permutations and k-subsets occupying consecutive circular positions.",
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        "r012:concept:erdos-ko-rado-theorem"
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      "source_label": "circle-permutation double counting",
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      "unit_ids": [
        "r012:unit:s_kitchensink_extremal-set-theory"
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    },
    {
      "concept_id": "r012:concept:clique",
      "definition": "A set of vertices that are pairwise adjacent.",
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        "r012:concept:adjacency"
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        "r012:unit:s_intro_graph",
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        "r012:unit:s_ramsey_probability",
        "r012:unit:s_ramsey_exercises"
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    {
      "concept_id": "r012:concept:clique-number",
      "definition": "The maximum cardinality of a clique in a graph.",
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        "r012:concept:clique"
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      "unit_ids": [
        "r012:unit:s_graphs_color"
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    },
    {
      "concept_id": "r012:concept:closed-form-expression",
      "definition": "An explicit expression for a function value that depends on the index rather than on earlier values of the function.",
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        "r012:concept:recurrence"
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        "r012:unit:ch_recurrence",
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        "r012:unit:ex_recurrence_deg4-repeated",
        "r012:unit:ex_recurrence_lines-solved"
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    },
    {
      "concept_id": "r012:concept:closed-interval",
      "definition": "A real interval containing both of its endpoints.",
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      "source_label": "closed interval",
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        "r012:unit:s_posets_intervalorder"
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    {
      "concept_id": "r012:concept:coin-change-generating-function",
      "definition": "An ordinary generating-function product whose coefficient counts unordered payments assembled from allowed coin denominations.",
      "prerequisite_concept_ids": [
        "r012:concept:ordinary-generating-function",
        "r012:concept:generating-function-distribution-model"
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        "r012:unit:auto:921b776e937d50a2fd4c2c37",
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      "concept_id": "r012:concept:collatz-sequence",
      "definition": "A positive-integer sequence formed by replacing an even term n by n/2 and an odd term n by 3n+1.",
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        "r012:concept:positive-integer",
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        "r012:unit:ex_collatz"
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    {
      "concept_id": "r012:concept:color-scheme",
      "definition": "The named set of colors used by the HTML presentation.",
      "prerequisite_concept_ids": [],
      "source_label": "color scheme",
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      "unit_ids": [
        "r012:unit:backmatter"
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    {
      "concept_id": "r012:concept:coloring-equivalence-under-action",
      "definition": "Two colorings are equivalent when an allowed transformation maps one to the other.",
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        "r012:concept:group-action",
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      "source_label": "coloring equivalence under an action",
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        "r012:unit:s_polya_square"
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    {
      "concept_id": "r012:concept:combination",
      "definition": "An unordered selection from a collection.",
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        "r012:concept:enumeration"
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      "source_label": "combination",
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        "r012:unit:s_strings_combinations",
        "r012:unit:prop_strings_binomraw",
        "r012:unit:prop_strings_symmetric"
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    {
      "concept_id": "r012:concept:combinatorial-proof",
      "definition": "A proof of an identity obtained by counting the same finite family in two different ways.",
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        "r012:concept:counting",
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        "r012:unit:s_strings_comb-proof"
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    {
      "concept_id": "r012:concept:combinatorics",
      "definition": "The study of finite or discrete structures, counting, construction, and optimization.",
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      "concept_id": "r012:concept:combinatorics-background-appendix",
      "definition": "A reference sequence covering sets, relations, number systems, order, and axiomatic foundations.",
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      "concept_id": "r012:concept:comparability-graph",
      "definition": "A graph joining exactly the distinct comparable pairs of a poset.",
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        "r012:concept:graph",
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        "r012:unit:fig_noncompgraph"
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    {
      "concept_id": "r012:concept:comparison-sorting",
      "definition": "A sorting model in which information about the input order is obtained through pairwise comparisons.",
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        "r012:concept:sorting"
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        "r012:unit:auto:e438802b2d5527a91381cbc2"
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      "concept_id": "r012:concept:complementary-set-pair",
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        "r012:concept:set-family"
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      "concept_id": "r012:concept:complete-bipartite-graph",
      "definition": "A bipartite graph containing every edge between its two vertex classes.",
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        "r012:concept:bipartite-graph",
        "r012:concept:complete-graph"
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        "r012:unit:fig_k44minus"
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      "concept_id": "r012:concept:complete-graph",
      "definition": "A simple graph in which every pair of distinct vertices is adjacent.",
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        "r012:concept:simple-graph",
        "r012:concept:adjacency"
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        "r012:unit:s_graphs_intro",
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      "concept_id": "r012:concept:complete-subgraph",
      "definition": "A subgraph in which every pair of distinct vertices is adjacent.",
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        "r012:concept:subgraph"
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        "r012:unit:auto:6691548129df37fcc64c5423"
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      "concept_id": "r012:concept:complex-number-system",
      "definition": "The Cartesian product R×R with componentwise addition and the standard complex multiplication rule.",
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        "r012:concept:real-number-as-cut",
        "r012:concept:cartesian-product"
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        "r012:unit:s_background_complex"
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    },
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      "concept_id": "r012:concept:computational-complexity",
      "definition": "The resources required by algorithms as a function of input size.",
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        "r012:concept:algorithm"
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        "r012:unit:ch_basics",
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        "r012:unit:s_basics_questions"
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    },
    {
      "concept_id": "r012:concept:computational-public-health",
      "definition": "Applying scientific analysis to public-health threats such as unfamiliar viruses.",
      "prerequisite_concept_ids": [],
      "source_label": "computational public health",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:computer-algebra-system",
      "definition": "Software for symbolic and exact mathematical computation.",
      "prerequisite_concept_ids": [
        "r012:concept:algorithm"
      ],
      "source_label": "computer algebra system",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_number"
      ]
    },
    {
      "concept_id": "r012:concept:computing-device",
      "definition": "A device capable of executing computational processes.",
      "prerequisite_concept_ids": [],
      "source_label": "computing device",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:conditional-probability",
      "definition": "For P(B)>0, the probability of A given B is P(A intersect B)/P(B).",
      "prerequisite_concept_ids": [
        "r012:concept:probability-space",
        "r012:concept:event"
      ],
      "source_label": "conditional probability",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:cf51ab7939254cfefade0b8c"
      ]
    },
    {
      "concept_id": "r012:concept:conditional-probability-application",
      "definition": "Using a conditioning context to distinguish comparisons made under different available-choice sets.",
      "prerequisite_concept_ids": [
        "r012:concept:conditional-probability"
      ],
      "source_label": "conditional probability as contextual reasoning",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_discussion"
      ]
    },
    {
      "concept_id": "r012:concept:connected-component",
      "definition": "A maximal connected subgraph.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-connectivity"
      ],
      "source_label": "component",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_graph",
        "r012:unit:fig_graphdata"
      ]
    },
    {
      "concept_id": "r012:concept:connected-poset",
      "definition": "A poset whose comparability graph is connected.",
      "prerequisite_concept_ids": [
        "r012:concept:comparability-graph",
        "r012:concept:graph-connectivity"
      ],
      "source_label": "connected poset",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:consecutive-term-ratio",
      "definition": "A quotient of the form f_(n+1)/f_n used to study the growth and limiting behavior of a sequence.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence"
      ],
      "source_label": "ratio of consecutive sequence terms",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_intro_fib",
        "r012:unit:tab_fib-ratios"
      ]
    },
    {
      "concept_id": "r012:concept:constant-coefficient-recurrence",
      "definition": "A linear recurrence equation whose coefficients do not depend on the sequence index.",
      "prerequisite_concept_ids": [
        "r012:concept:linear-recurrence-equation"
      ],
      "source_label": "linear recurrence equation with constant coefficients",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_linear",
        "r012:unit:rq-recurrence_linear-matching",
        "r012:unit:s_recurrence_adv-ops_const-coeff",
        "r012:unit:eqn_advance",
        "r012:unit:s_recurrence_adv-ops_roots-factors",
        "r012:unit:s_recurrence_adv-ops_zero",
        "r012:unit:rq-recurrence_adv-ops_rewrite"
      ]
    },
    {
      "concept_id": "r012:concept:constrained-minimum-spanning-network",
      "definition": "A minimum-cost connected network problem in which specified edges must be included before the remaining safe edges are selected.",
      "prerequisite_concept_ids": [
        "r012:concept:minimum-spanning-tree"
      ],
      "source_label": "minimum spanning network with mandatory edges",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:context-dependent-preference",
      "definition": "A preference between two alternatives that can change when a third alternative is present or absent.",
      "prerequisite_concept_ids": [
        "r012:concept:conditional-probability"
      ],
      "source_label": "context-dependent preference",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_discussion"
      ]
    },
    {
      "concept_id": "r012:concept:countably-infinite-sample-space",
      "definition": "A sample space whose outcomes can be enumerated, so singleton masses form an absolutely convergent sum equal to one.",
      "prerequisite_concept_ids": [
        "r012:concept:sample-space",
        "r012:concept:infinite-series"
      ],
      "source_label": "countably infinite sample space",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_infinite-outcomes"
      ]
    },
    {
      "concept_id": "r012:concept:counting",
      "definition": "Determining the cardinality of a finite family of outcomes or structures.",
      "prerequisite_concept_ids": [
        "r012:concept:enumeration"
      ],
      "source_label": "counting",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_enum",
        "r012:unit:s_inclusion-exclusion_PI",
        "r012:unit:inclusion-exclusion_PI_IE-sum-terms",
        "r012:unit:inclusion-exclusion_PI_functions-count",
        "r012:unit:inclusion-exclusion_PI_perms-count"
      ]
    },
    {
      "concept_id": "r012:concept:cover-graph",
      "definition": "The undirected graph whose edges are the cover relations of a poset.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:cover-relation"
      ],
      "source_label": "cover graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:cover-relation",
      "definition": "An ordered pair x<y with no element strictly between x and y.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order"
      ],
      "source_label": "cover relation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro"
      ]
    },
    {
      "concept_id": "r012:concept:covering",
      "definition": "A family of objects whose union or incidence covers a required ground structure.",
      "prerequisite_concept_ids": [
        "r012:concept:discrete-structures"
      ],
      "source_label": "covering",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro"
      ]
    },
    {
      "concept_id": "r012:concept:cube-face-coloring",
      "definition": "Counting colorings of cube faces modulo spatial rotations.",
      "prerequisite_concept_ids": [
        "r012:concept:group-action",
        "r012:concept:polya-enumeration-theorem"
      ],
      "source_label": "cube-face coloring",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:current-flow",
      "definition": "The feasible network flow being modified at the current stage of an augmenting-path algorithm.",
      "prerequisite_concept_ids": [
        "r012:concept:network-flow"
      ],
      "source_label": "current flow",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_augmenting"
      ]
    },
    {
      "concept_id": "r012:concept:cut-arithmetic",
      "definition": "Addition is pointwise, order is inclusion, and positive multiplication is generated from nonnegative products.",
      "prerequisite_concept_ids": [
        "r012:concept:dedekind-cut",
        "r012:concept:rational-arithmetic"
      ],
      "source_label": "arithmetic and order of cuts",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_reals"
      ]
    },
    {
      "concept_id": "r012:concept:cut-capacity",
      "definition": "The sum of capacities of directed edges from the source side L to the sink side U of a cut.",
      "prerequisite_concept_ids": [
        "r012:concept:network-cut",
        "r012:concept:edge-capacity"
      ],
      "source_label": "capacity of a cut",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_flows-cuts",
        "r012:unit:s_networkflow_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:cutting-head",
      "definition": "A moving cutting component whose path can be optimized in manufacturing.",
      "prerequisite_concept_ids": [
        "r012:concept:industrial-optimization"
      ],
      "source_label": "cutting head",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:cycle",
      "definition": "A closed path whose internal vertices are distinct.",
      "prerequisite_concept_ids": [
        "r012:concept:path"
      ],
      "source_label": "cycle",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_graph",
        "r012:unit:auto:21546ae1bdf04f7552481516"
      ]
    },
    {
      "concept_id": "r012:concept:cycle-index",
      "definition": "The group average of monomials encoding the cycle-length structure of each permutation.",
      "prerequisite_concept_ids": [
        "r012:concept:permutation-group",
        "r012:concept:cycle-notation",
        "r012:concept:burnside-lemma"
      ],
      "source_label": "cycle index",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_polya"
      ]
    },
    {
      "concept_id": "r012:concept:cycle-notation",
      "definition": "A representation of a permutation as ordered disjoint cycles.",
      "prerequisite_concept_ids": [
        "r012:concept:permutation"
      ],
      "source_label": "cycle notation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_perm-groups"
      ]
    },
    {
      "concept_id": "r012:concept:cyclic-group",
      "definition": "A group generated by repeated powers of one element.",
      "prerequisite_concept_ids": [
        "r012:concept:group",
        "r012:concept:permutation-group"
      ],
      "source_label": "cyclic group",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:database-identifier-recurrence",
      "definition": "A recurrence obtained from disjoint prefix rules of lengths one and two for valid identifiers.",
      "prerequisite_concept_ids": [
        "r012:concept:string",
        "r012:concept:recurrence-relation"
      ],
      "source_label": "recurrence for recursively constructed database identifiers",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:7126d6d352834b81eac3866d"
      ]
    },
    {
      "concept_id": "r012:concept:decimal-expansion",
      "definition": "A finite or infinite digit expansion of a real number after the decimal point.",
      "prerequisite_concept_ids": [
        "r012:concept:real-number-as-cut",
        "r012:concept:positional-base-notation"
      ],
      "source_label": "decimal expansion",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_complex"
      ]
    },
    {
      "concept_id": "r012:concept:decreasing-subsequence",
      "definition": "A subsequence whose terms decrease in their inherited order.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence"
      ],
      "source_label": "decreasing subsequence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_ErdosSzekeres",
        "r012:unit:s_basics_exact"
      ]
    },
    {
      "concept_id": "r012:concept:dedekind-cut",
      "definition": "A nonempty proper downward-closed subset of the rationals with no greatest element.",
      "prerequisite_concept_ids": [
        "r012:concept:rational-number",
        "r012:concept:total-order"
      ],
      "source_label": "Dedekind cut",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_reals"
      ]
    },
    {
      "concept_id": "r012:concept:deferred-acceptance-algorithm",
      "definition": "Proposers advance down preference lists while receivers retain their most-preferred proposal so far.",
      "prerequisite_concept_ids": [
        "r012:concept:stable-matching"
      ],
      "source_label": "deferred acceptance algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_stable-match"
      ]
    },
    {
      "concept_id": "r012:concept:degenerate-interval",
      "definition": "A closed interval whose left and right endpoints coincide.",
      "prerequisite_concept_ids": [
        "r012:concept:closed-interval"
      ],
      "source_label": "degenerate interval",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intervalorder"
      ]
    },
    {
      "concept_id": "r012:concept:degree-sequence",
      "definition": "The vertex degrees of a graph listed in nonincreasing order.",
      "prerequisite_concept_ids": [
        "r012:concept:vertex-degree",
        "r012:concept:sequence"
      ],
      "source_label": "degree sequence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ex_graphs_degseq",
        "r012:unit:ex_graphs_degseq2"
      ]
    },
    {
      "concept_id": "r012:concept:denominator",
      "definition": "The lower component of a fraction, required to be nonzero when the fraction represents a rational number.",
      "prerequisite_concept_ids": [
        "r012:concept:fraction"
      ],
      "source_label": "denominator",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:dependency-neighborhood",
      "definition": "A designated family containing every event on which an event may depend.",
      "prerequisite_concept_ids": [
        "r012:concept:independent-events"
      ],
      "source_label": "dependency neighborhood",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_lovasz-local",
        "r012:unit:s_kitchensink_applying-local-lemma"
      ]
    },
    {
      "concept_id": "r012:concept:dependent-events",
      "definition": "Events that are not independent.",
      "prerequisite_concept_ids": [
        "r012:concept:independent-events"
      ],
      "source_label": "dependent events",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:e890493d9ce5282dd02dd98c"
      ]
    },
    {
      "concept_id": "r012:concept:derangement",
      "definition": "A permutation that fixes none of the objects it rearranges.",
      "prerequisite_concept_ids": [
        "r012:concept:permutation"
      ],
      "source_label": "derangement",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_inclusion-exclusion",
        "r012:unit:exa_inclusion-exclusion_prop-derange",
        "r012:unit:s_inclusion-exclusion_derangements",
        "r012:unit:auto:efc19c37945fe17ccd593b42",
        "r012:unit:auto:dec906b7a981dd80a50fb0a2",
        "r012:unit:auto:0ccd82df017d6432c7a435f0",
        "r012:unit:auto:57a1c249f2782f556231221b",
        "r012:unit:auto:3ac47f248ab24d08c8fbed2f",
        "r012:unit:auto:0faa5a1d42e8503171d0a48a"
      ]
    },
    {
      "concept_id": "r012:concept:derangement-asymptotic-probability",
      "definition": "The fraction d_n/n! of permutations of [n] that have no fixed points approaches 1/e as n tends to infinity.",
      "prerequisite_concept_ids": [
        "r012:concept:derangement"
      ],
      "source_label": "asymptotic probability of a derangement",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:57a1c249f2782f556231221b",
        "r012:unit:auto:3ac47f248ab24d08c8fbed2f"
      ]
    },
    {
      "concept_id": "r012:concept:derangement-enumeration-formula",
      "definition": "The inclusion-exclusion formula d_n=sum from k=0 to n of (-1)^k binom(n,k)(n-k)! for permutations of [n] with no fixed points.",
      "prerequisite_concept_ids": [
        "r012:concept:derangement",
        "r012:concept:inclusion-exclusion"
      ],
      "source_label": "derangement enumeration formula",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_inclusion-exclusion_derangements",
        "r012:unit:auto:0ccd82df017d6432c7a435f0"
      ]
    },
    {
      "concept_id": "r012:concept:derangement-probability",
      "definition": "The probability that a uniformly random permutation has no fixed points.",
      "prerequisite_concept_ids": [
        "r012:concept:derangement",
        "r012:concept:equally-likely-outcomes"
      ],
      "source_label": "probability of a derangement",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:f6784d3449a3d1a00f4c7855"
      ]
    },
    {
      "concept_id": "r012:concept:digit",
      "definition": "A symbol representing a natural number strictly below the base.",
      "prerequisite_concept_ids": [
        "r012:concept:positional-base-notation"
      ],
      "source_label": "digit",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_decimal"
      ]
    },
    {
      "concept_id": "r012:concept:digraph",
      "definition": "A graph whose edges carry directions.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "digraph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro"
      ]
    },
    {
      "concept_id": "r012:concept:dihedral-group",
      "definition": "The permutation group generated by rotations and reflections of a regular polygon.",
      "prerequisite_concept_ids": [
        "r012:concept:permutation-group"
      ],
      "source_label": "dihedral group",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_perm-groups"
      ]
    },
    {
      "concept_id": "r012:concept:dijkstra-algorithm",
      "definition": "A nonnegative-weight shortest-path algorithm that permanently labels the temporary vertex of least current distance and relaxes outgoing candidates.",
      "prerequisite_concept_ids": [
        "r012:concept:directed-distance"
      ],
      "source_label": "Dijkstra's algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:alg_dijkstra"
      ]
    },
    {
      "concept_id": "r012:concept:dijkstra-negative-weight-failure",
      "definition": "Negative weights invalidate permanent-label reasoning, and adding a uniform constant can change which path has minimum total weight because paths may use different numbers of edges.",
      "prerequisite_concept_ids": [
        "r012:concept:dijkstra-nonnegative-correctness"
      ],
      "source_label": "failure of Dijkstra's algorithm with negative weights",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:dijkstra-nonnegative-correctness",
      "definition": "With nonnegative directed-edge weights, the final delta and path records give a shortest path to every reachable vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:dijkstra-relaxation",
        "r012:concept:shortest-path-subpath-optimality",
        "r012:concept:dijkstra-permanent-distance-monotonicity"
      ],
      "source_label": "correctness of Dijkstra's algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_shortest-paths"
      ]
    },
    {
      "concept_id": "r012:concept:dijkstra-permanent-distance-monotonicity",
      "definition": "Vertices become permanent in nondecreasing order of their delta values.",
      "prerequisite_concept_ids": [
        "r012:concept:dijkstra-algorithm"
      ],
      "source_label": "monotonicity of permanent labels",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_shortest-paths"
      ]
    },
    {
      "concept_id": "r012:concept:dijkstra-relaxation",
      "definition": "Replace delta(x) by the minimum of its current value and delta(v_i)+w(v_i,x), updating the stored path if the value decreases.",
      "prerequisite_concept_ids": [
        "r012:concept:dijkstra-algorithm"
      ],
      "source_label": "Dijkstra distance update",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:alg_dijkstra"
      ]
    },
    {
      "concept_id": "r012:concept:dilworth-theorem",
      "definition": "The minimum number of chains in a partition of a finite poset equals its width.",
      "prerequisite_concept_ids": [
        "r012:concept:chain-partition",
        "r012:concept:poset-width"
      ],
      "source_label": "Dilworth's theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_dilworth",
        "r012:unit:para_posets_dilworth_proof",
        "r012:unit:s_flowapplications_chain-partition"
      ]
    },
    {
      "concept_id": "r012:concept:dirac-theorem",
      "definition": "A sufficient condition for Hamiltonicity: an n-vertex graph with n at least three and minimum degree at least n/2 is Hamiltonian.",
      "prerequisite_concept_ids": [
        "r012:concept:hamiltonian-graph",
        "r012:concept:vertex-degree"
      ],
      "source_label": "Dirac's theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_graphs_dirac"
      ]
    },
    {
      "concept_id": "r012:concept:directed-cycle",
      "definition": "A directed path together with a directed edge from its last vertex back to its first vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:directed-path"
      ],
      "source_label": "directed cycle",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_digraphs"
      ]
    },
    {
      "concept_id": "r012:concept:directed-distance",
      "definition": "The minimum length of a directed path from the designated root to a vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:directed-path-length"
      ],
      "source_label": "distance in a digraph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_shortest-paths"
      ]
    },
    {
      "concept_id": "r012:concept:directed-edge",
      "definition": "An ordered pair of distinct vertices representing an edge from its first vertex to its second.",
      "prerequisite_concept_ids": [
        "r012:concept:digraph"
      ],
      "source_label": "directed edge",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_digraphs",
        "r012:unit:s_networkflow_intro",
        "r012:unit:s_networkflow_flows-cuts",
        "r012:unit:s_networkflow_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:directed-path",
      "definition": "A sequence of distinct vertices in which every consecutive ordered pair is a directed edge.",
      "prerequisite_concept_ids": [
        "r012:concept:directed-edge"
      ],
      "source_label": "directed path",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_digraphs"
      ]
    },
    {
      "concept_id": "r012:concept:directed-path-length",
      "definition": "The sum of the lengths of the directed edges traversed by a path.",
      "prerequisite_concept_ids": [
        "r012:concept:weighted-digraph"
      ],
      "source_label": "length of a directed path",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_shortest-paths"
      ]
    },
    {
      "concept_id": "r012:concept:disconnected-graph",
      "definition": "A graph that has more than one connected component.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-connectivity"
      ],
      "source_label": "disconnected graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_graph",
        "r012:unit:fig_graphdata"
      ]
    },
    {
      "concept_id": "r012:concept:discrete-structures",
      "definition": "Finite or countable structures such as graphs, posets, strings, designs, distributions, coverings, and partitions.",
      "prerequisite_concept_ids": [
        "r012:concept:combinatorics"
      ],
      "source_label": "discrete structures",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro"
      ]
    },
    {
      "concept_id": "r012:concept:disjoint-events",
      "definition": "Events whose intersection is empty.",
      "prerequisite_concept_ids": [
        "r012:concept:event"
      ],
      "source_label": "disjoint events",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:exa_twojars"
      ]
    },
    {
      "concept_id": "r012:concept:disjoint-poset-sum",
      "definition": "A poset formed from disjoint component posets with no comparisons between different components.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-component"
      ],
      "source_label": "disjoint sum of posets",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intervalorder"
      ]
    },
    {
      "concept_id": "r012:concept:distinct-part-partition",
      "definition": "An integer partition in which no positive part occurs more than once.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-partition"
      ],
      "source_label": "partition into distinct parts",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:fig_genfunction_partsof8",
        "r012:unit:thm_partition",
        "r012:unit:auto:c1cbbffbb5bf258ea18be45d",
        "r012:unit:s_genfunction_discussion",
        "r012:unit:auto:c53a9727c6ac71ed663831ee",
        "r012:unit:auto:5a5a5f490053509f506e2e65"
      ]
    },
    {
      "concept_id": "r012:concept:distinct-root-recurrence-solution",
      "definition": "When p(A) factors into distinct nonzero linear factors A-r_i, every solution is a linear combination of the exponential sequences r_i^n.",
      "prerequisite_concept_ids": [
        "r012:concept:particular-plus-homogeneous-solution",
        "r012:concept:advancement-operator-polynomial"
      ],
      "source_label": "distinct-root solution of a homogeneous recurrence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:c52c9183ba4135b30d2552a6",
        "r012:unit:eqn_distinct",
        "r012:unit:auto:0521558e3324b301583e231e",
        "r012:unit:eqn_distinct2",
        "r012:unit:eqn_distinct3",
        "r012:unit:ex_recurrence_deg2",
        "r012:unit:ex_recurrence_ternary-strings-no-20-solved",
        "r012:unit:auto:6fb2d3d14bf9ef34219de62c",
        "r012:unit:ex_recurrence_deg4-repeated"
      ]
    },
    {
      "concept_id": "r012:concept:distinguishing-interval-representation",
      "definition": "An interval representation in which all interval endpoints are distinct.",
      "prerequisite_concept_ids": [
        "r012:concept:interval-representation",
        "r012:concept:interval-endpoint"
      ],
      "source_label": "distinguishing representation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intervalorder"
      ]
    },
    {
      "concept_id": "r012:concept:distribution",
      "definition": "Assignment of objects to recipients or cells under stated distinguishability and occupancy constraints.",
      "prerequisite_concept_ids": [
        "r012:concept:enumeration"
      ],
      "source_label": "distribution of objects into cells",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_enum",
        "r012:unit:s_genfunction_distributions"
      ]
    },
    {
      "concept_id": "r012:concept:distribution-cell",
      "definition": "A recipient, box, or category to which an object may be assigned.",
      "prerequisite_concept_ids": [
        "r012:concept:distribution"
      ],
      "source_label": "cell in a distribution problem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_enum"
      ]
    },
    {
      "concept_id": "r012:concept:divisibility",
      "definition": "An integer n divides an integer m when m is an integer multiple of n.",
      "prerequisite_concept_ids": [],
      "source_label": "divides",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_gcd",
        "r012:unit:exa_inclusion-exclusion_prop-divis",
        "r012:unit:prop_num-divisible"
      ]
    },
    {
      "concept_id": "r012:concept:divisibility-count-for-primes",
      "definition": "For distinct primes p_1 through p_k dividing n, exactly n/(p_1...p_k) integers from 1 through n are divisible by all of them.",
      "prerequisite_concept_ids": [
        "r012:concept:divisibility",
        "r012:concept:prime-factorization"
      ],
      "source_label": "count of integers divisible by given prime divisors",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:prop_num-divisible"
      ]
    },
    {
      "concept_id": "r012:concept:division",
      "definition": "The inverse operation to multiplication when the divisor is invertible and nonzero.",
      "prerequisite_concept_ids": [
        "r012:concept:binary-operation"
      ],
      "source_label": "division",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:division-algorithm",
      "definition": "For d>0, every n has unique q and r satisfying n=qd+r and 0≤r<d.",
      "prerequisite_concept_ids": [
        "r012:concept:natural-number-order",
        "r012:concept:integer-multiplication"
      ],
      "source_label": "division algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_decimal"
      ]
    },
    {
      "concept_id": "r012:concept:document-class",
      "definition": "The LaTeX class controlling the document's structural typesetting.",
      "prerequisite_concept_ids": [],
      "source_label": "document class",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:backmatter"
      ]
    },
    {
      "concept_id": "r012:concept:down-set",
      "definition": "A set of elements lying strictly or weakly below a specified element or subset, according to the indicated notation.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order"
      ],
      "source_label": "down set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:para_posets_dilworth_proof"
      ]
    },
    {
      "concept_id": "r012:concept:dual-dilworth-theorem",
      "definition": "The minimum number of antichains in a partition of a finite poset equals its height.",
      "prerequisite_concept_ids": [
        "r012:concept:antichain-partition",
        "r012:concept:poset-height"
      ],
      "source_label": "dual of Dilworth's theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_dualdilworth"
      ]
    },
    {
      "concept_id": "r012:concept:dual-integer-partition",
      "definition": "The conjugate partition whose j-th part counts original parts of size at least j.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-partition"
      ],
      "source_label": "dual integer partition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_zero-one-matrices"
      ]
    },
    {
      "concept_id": "r012:concept:dual-poset",
      "definition": "The poset obtained by reversing every ordered comparison.",
      "prerequisite_concept_ids": [
        "r012:concept:poset"
      ],
      "source_label": "dual poset",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:edge",
      "definition": "A two-element subset of the vertex set of a simple graph.",
      "prerequisite_concept_ids": [
        "r012:concept:vertex"
      ],
      "source_label": "edge",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_graph",
        "r012:unit:fig_graphdata",
        "r012:unit:fig_connectedgraph",
        "r012:unit:s_networkflow_intro",
        "r012:unit:s_networkflow_flows-cuts",
        "r012:unit:s_networkflow_augmenting",
        "r012:unit:alg_labeling",
        "r012:unit:s_networkflow_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:edge-capacity",
      "definition": "A nonnegative upper bound on the amount of flow carried by a directed edge.",
      "prerequisite_concept_ids": [
        "r012:concept:flow-network"
      ],
      "source_label": "edge capacity",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_intro"
      ]
    },
    {
      "concept_id": "r012:concept:edge-crossing",
      "definition": "An intersection of drawn edge interiors that is not necessarily a vertex of the graph.",
      "prerequisite_concept_ids": [
        "r012:concept:edge",
        "r012:concept:geometry"
      ],
      "source_label": "edge crossing",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_geom",
        "r012:unit:fig_crossingedges"
      ]
    },
    {
      "concept_id": "r012:concept:edge-flow-status",
      "definition": "Classification of a directed edge according to whether its flow is positive, equals capacity, or is zero.",
      "prerequisite_concept_ids": [
        "r012:concept:network-flow",
        "r012:concept:edge"
      ],
      "source_label": "used, full, and empty edges",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_augmenting"
      ]
    },
    {
      "concept_id": "r012:concept:element",
      "definition": "An object belonging to a set.",
      "prerequisite_concept_ids": [
        "r012:concept:set"
      ],
      "source_label": "set element",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_intro"
      ]
    },
    {
      "concept_id": "r012:concept:elementary-outcome",
      "definition": "One individual outcome in a sample space.",
      "prerequisite_concept_ids": [
        "r012:concept:outcome"
      ],
      "source_label": "elementary outcome",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_intro"
      ]
    },
    {
      "concept_id": "r012:concept:elementary-subdivision",
      "definition": "Replacement of one graph edge by a two-edge path through a new degree-two vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:edge",
        "r012:concept:path"
      ],
      "source_label": "elementary subdivision",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_planar"
      ]
    },
    {
      "concept_id": "r012:concept:empty-set",
      "definition": "The unique set containing no elements.",
      "prerequisite_concept_ids": [
        "r012:concept:set-membership"
      ],
      "source_label": "empty set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_int-union"
      ]
    },
    {
      "concept_id": "r012:concept:empty-set-axiom",
      "definition": "There exists a set having no elements.",
      "prerequisite_concept_ids": [
        "r012:concept:zfc-set-theory"
      ],
      "source_label": "empty-set axiom",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_ZFC"
      ]
    },
    {
      "concept_id": "r012:concept:enumeration",
      "definition": "Counting arrangements, selections, distributions, and equivalence classes of discrete objects.",
      "prerequisite_concept_ids": [
        "r012:concept:combinatorics"
      ],
      "source_label": "enumeration",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:s_intro_enum"
      ]
    },
    {
      "concept_id": "r012:concept:epilogue",
      "definition": "A closing narrative that follows the characters after graduation.",
      "prerequisite_concept_ids": [],
      "source_label": "epilogue",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:equally-likely-outcomes",
      "definition": "Outcomes assigned the same singleton probability.",
      "prerequisite_concept_ids": [
        "r012:concept:outcome",
        "r012:concept:probability-measure"
      ],
      "source_label": "equally likely outcomes",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:33c963d4a1733b8680bf29a7",
        "r012:unit:auto:dc7056216e439071dc1ede50"
      ]
    },
    {
      "concept_id": "r012:concept:equivalence-class",
      "definition": "The set of all elements equivalent to a specified element under an equivalence relation.",
      "prerequisite_concept_ids": [
        "r012:concept:equivalence-relation",
        "r012:concept:set-partition"
      ],
      "source_label": "equivalence class",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_burnside",
        "r012:unit:s_background_equivalence"
      ]
    },
    {
      "concept_id": "r012:concept:equivalence-relation",
      "definition": "A binary relation that is reflexive, symmetric, and transitive.",
      "prerequisite_concept_ids": [
        "r012:concept:symmetric-relation",
        "r012:concept:reflexive-relation",
        "r012:concept:transitive-relation"
      ],
      "source_label": "equivalence relation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_exercises",
        "r012:unit:s_background_equivalence"
      ]
    },
    {
      "concept_id": "r012:concept:erdos-high-girth-high-chromatic-theorem",
      "definition": "For any girth and chromatic thresholds, a graph exists whose girth and chromatic number exceed them.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-girth",
        "r012:concept:chromatic-number",
        "r012:concept:probabilistic-method"
      ],
      "source_label": "Erdos high-girth high-chromatic theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_girth"
      ]
    },
    {
      "concept_id": "r012:concept:erdos-ko-rado-theorem",
      "definition": "A pairwise-intersecting family of k-subsets of [n], n at least 2k, has size at most binomial(n-1,k-1).",
      "prerequisite_concept_ids": [
        "r012:concept:intersecting-set-family"
      ],
      "source_label": "Erdős–Ko–Rado theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_extremal-set-theory"
      ]
    },
    {
      "concept_id": "r012:concept:erdos-renyi-random-graph",
      "definition": "A graph formed by including each possible edge independently with probability one half.",
      "prerequisite_concept_ids": [
        "r012:concept:independent-events",
        "r012:concept:graph"
      ],
      "source_label": "independent-edge random graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:6691548129df37fcc64c5423"
      ]
    },
    {
      "concept_id": "r012:concept:euclidean-algorithm",
      "definition": "A recursive remainder algorithm for computing the greatest common divisor.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-division",
        "r012:concept:greatest-common-divisor",
        "r012:concept:recursion"
      ],
      "source_label": "Euclidean Algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_euclideanalg"
      ]
    },
    {
      "concept_id": "r012:concept:euler-partition-theorem",
      "definition": "For every positive n, the number of partitions of n into distinct parts equals the number of partitions of n into odd parts.",
      "prerequisite_concept_ids": [
        "r012:concept:distinct-part-partition",
        "r012:concept:odd-part-partition",
        "r012:concept:partition-generating-function"
      ],
      "source_label": "Euler's distinct-parts and odd-parts partition theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_partition",
        "r012:unit:auto:c1cbbffbb5bf258ea18be45d",
        "r012:unit:s_genfunction_discussion",
        "r012:unit:auto:c53a9727c6ac71ed663831ee"
      ]
    },
    {
      "concept_id": "r012:concept:euler-phi-function",
      "definition": "The arithmetic function that counts positive integers not exceeding n that are relatively prime to n.",
      "prerequisite_concept_ids": [
        "r012:concept:inclusion-exclusion",
        "r012:concept:greatest-common-divisor",
        "r012:concept:prime-factorization"
      ],
      "source_label": "Euler phi-function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_inclusion-exclusion",
        "r012:unit:s_inclusion-exclusion_euler-phi",
        "r012:unit:thm_eulerphi",
        "r012:unit:eq_eulerphi",
        "r012:unit:auto:5cf98fb376a04e75419df1f9",
        "r012:unit:auto:78cd58d5f8395977c731d2e1"
      ]
    },
    {
      "concept_id": "r012:concept:euler-phi-product-formula",
      "definition": "If the distinct prime divisors of n are p_1 through p_m, then phi(n)=n times the product of (p_i-1)/p_i.",
      "prerequisite_concept_ids": [
        "r012:concept:euler-phi-function",
        "r012:concept:prime-factorization",
        "r012:concept:inclusion-exclusion"
      ],
      "source_label": "Euler phi product formula",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_eulerphi",
        "r012:unit:eq_eulerphi",
        "r012:unit:auto:40c708c69ade17788d6a5947"
      ]
    },
    {
      "concept_id": "r012:concept:euler-planar-formula",
      "definition": "For a connected planar drawing with n vertices, m edges, and f faces, n-m+f=2.",
      "prerequisite_concept_ids": [
        "r012:concept:planar-drawing",
        "r012:concept:graph-face"
      ],
      "source_label": "Euler's Formula",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_planar"
      ]
    },
    {
      "concept_id": "r012:concept:eulerian-circuit",
      "definition": "A circuit that traverses every edge of a graph exactly once.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-circuit",
        "r012:concept:edge"
      ],
      "source_label": "eulerian circuit",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_eulerham",
        "r012:unit:alg-eulerian",
        "r012:unit:fig_graphs_eulerexample"
      ]
    },
    {
      "concept_id": "r012:concept:eulerian-graph",
      "definition": "A graph possessing an Eulerian circuit.",
      "prerequisite_concept_ids": [
        "r012:concept:eulerian-circuit",
        "r012:concept:graph-connectivity",
        "r012:concept:vertex-degree"
      ],
      "source_label": "eulerian graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_eulerham",
        "r012:unit:thm_eulerian",
        "r012:unit:alg-eulerian"
      ]
    },
    {
      "concept_id": "r012:concept:eulerian-tour",
      "definition": "A closed traversal that uses every edge of a graph exactly once.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:path"
      ],
      "source_label": "tour using every edge exactly once",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_opt"
      ]
    },
    {
      "concept_id": "r012:concept:eulerian-trail",
      "definition": "A trail traversing every edge exactly once without requiring the endpoints to coincide.",
      "prerequisite_concept_ids": [
        "r012:concept:eulerian-circuit",
        "r012:concept:graph-walk"
      ],
      "source_label": "Eulerian trail",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:even-symbol-count-filter",
      "definition": "The factor (e^x+e^(-x))/2, which retains exactly the even symbol-count terms of an exponential generating function.",
      "prerequisite_concept_ids": [
        "r012:concept:exponential-generating-function"
      ],
      "source_label": "even symbol-count exponential generating-function filter",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:7db46e9144887cfe4587f1aa",
        "r012:unit:ex_genfunction_exponential_passcode",
        "r012:unit:auto:cd91522cddb9cb10442a7836",
        "r012:unit:auto:f3edcd631926927e1e6b9719",
        "r012:unit:auto:fdf77306cd6d226cfda10c55",
        "r012:unit:genfunction_PI_string-restrict-2"
      ]
    },
    {
      "concept_id": "r012:concept:event",
      "definition": "A subset of the outcome set in a probability space.",
      "prerequisite_concept_ids": [
        "r012:concept:probability-space"
      ],
      "source_label": "event",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_intro",
        "r012:unit:s_kitchensink_lovasz-local"
      ]
    },
    {
      "concept_id": "r012:concept:event-complement",
      "definition": "The event consisting of all outcomes not contained in a specified event.",
      "prerequisite_concept_ids": [
        "r012:concept:event"
      ],
      "source_label": "event complement",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_lovasz-local"
      ]
    },
    {
      "concept_id": "r012:concept:event-complement-product-notation",
      "definition": "Concatenated event products denote intersections, with overbars denoting complements.",
      "prerequisite_concept_ids": [
        "r012:concept:event"
      ],
      "source_label": "event-complement product notation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_lovasz-local"
      ]
    },
    {
      "concept_id": "r012:concept:exact-solution",
      "definition": "A result that determines the precise value or best-possible threshold rather than only an approximation.",
      "prerequisite_concept_ids": [
        "r012:concept:combinatorics"
      ],
      "source_label": "exact solution",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_exact"
      ]
    },
    {
      "concept_id": "r012:concept:existential-quantifier",
      "definition": "The logical quantifier asserting that at least one object satisfies a predicate.",
      "prerequisite_concept_ids": [
        "r012:concept:logical-quantifier"
      ],
      "source_label": "existential quantifier",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_notation"
      ]
    },
    {
      "concept_id": "r012:concept:expected-bernoulli-success-count",
      "definition": "The expected number of successes in n Bernoulli trials with success probability p is np.",
      "prerequisite_concept_ids": [
        "r012:concept:linearity-of-expectation",
        "r012:concept:bernoulli-trials"
      ],
      "source_label": "expected number of successes in Bernoulli trials",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:f4036c5496787d4bb754e7c7"
      ]
    },
    {
      "concept_id": "r012:concept:expected-value",
      "definition": "The probability-weighted sum of a random variable's values.",
      "prerequisite_concept_ids": [
        "r012:concept:random-variable",
        "r012:concept:probability-measure"
      ],
      "source_label": "expectation of a random variable",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:fa26c80a67c89c43da03624e",
        "r012:unit:s_ramsey_probability",
        "r012:unit:thm_girth"
      ]
    },
    {
      "concept_id": "r012:concept:explicit-recurrence-solution",
      "definition": "A formula for a recurrence sequence term that depends directly on the index rather than recursively on earlier values.",
      "prerequisite_concept_ids": [
        "r012:concept:recurrence-relation"
      ],
      "source_label": "explicit nonrecursive solution of a recurrence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_discussion",
        "r012:unit:recurrence_discussion_takeaways"
      ]
    },
    {
      "concept_id": "r012:concept:exponent-laws",
      "definition": "Addition of exponents under multiplication and multiplication of exponents under iterated powers.",
      "prerequisite_concept_ids": [
        "r012:concept:restricted-exponentiation",
        "r012:concept:multiplication-laws"
      ],
      "source_label": "laws of exponents",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_exp"
      ]
    },
    {
      "concept_id": "r012:concept:exponential-generating-function",
      "definition": "A generating function of the form sum from n=0 to infinity of a_n x^n/n! for a sequence a_n.",
      "prerequisite_concept_ids": [
        "r012:concept:generating-function",
        "r012:concept:power-series",
        "r012:concept:factorial"
      ],
      "source_label": "exponential generating function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_exponential",
        "r012:unit:auto:a92a089aa7a8dd70c223b7f8",
        "r012:unit:auto:7db46e9144887cfe4587f1aa",
        "r012:unit:auto:3259ae9833c0290eb6d05545",
        "r012:unit:auto:4b9b577c7e32e0494cb91c36",
        "r012:unit:ex_genfunction_exponential_passcode",
        "r012:unit:rqs-genfunction_exponential",
        "r012:unit:rq-genfunction_exponential_passcode",
        "r012:unit:s_genfunction_exercises",
        "r012:unit:auto:036523eaa2d61e9332b741a9",
        "r012:unit:auto:cf2c41b37a21c756eb8fd9bc",
        "r012:unit:auto:7bf7f50248eb334f48c18d4f",
        "r012:unit:auto:cd91522cddb9cb10442a7836",
        "r012:unit:auto:f3edcd631926927e1e6b9719",
        "r012:unit:auto:fdf77306cd6d226cfda10c55",
        "r012:unit:auto:39ab9828f6c93359abfbc514",
        "r012:unit:s_genfunction_PI",
        "r012:unit:genfunction_PI_exponential-vs-ordinary",
        "r012:unit:genfunction_PI_string-restrict-4",
        "r012:unit:genfunction_PI_string-restrict-2"
      ]
    },
    {
      "concept_id": "r012:concept:exponential-generating-function-coefficient-extraction",
      "definition": "Recovery of a_n from the coefficient of x^n/n! in an exponential generating function, including closed-form filters for symbol restrictions.",
      "prerequisite_concept_ids": [
        "r012:concept:exponential-generating-function"
      ],
      "source_label": "coefficient extraction from an exponential generating function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:036523eaa2d61e9332b741a9",
        "r012:unit:auto:cf2c41b37a21c756eb8fd9bc",
        "r012:unit:auto:7bf7f50248eb334f48c18d4f",
        "r012:unit:auto:cd91522cddb9cb10442a7836",
        "r012:unit:auto:f3edcd631926927e1e6b9719",
        "r012:unit:auto:fdf77306cd6d226cfda10c55",
        "r012:unit:auto:39ab9828f6c93359abfbc514"
      ]
    },
    {
      "concept_id": "r012:concept:exponential-time",
      "definition": "Running time that grows exponentially with input size.",
      "prerequisite_concept_ids": [
        "r012:concept:computational-complexity",
        "r012:concept:big-o"
      ],
      "source_label": "exponential time",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_complexity"
      ]
    },
    {
      "concept_id": "r012:concept:extremal-family",
      "definition": "A set family attaining a maximum or minimum size under specified constraints.",
      "prerequisite_concept_ids": [
        "r012:concept:set-family"
      ],
      "source_label": "extremal family",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_extremal-set-theory"
      ]
    },
    {
      "concept_id": "r012:concept:extremal-set-theory",
      "definition": "The study of maximum or minimum family sizes under set-system constraints.",
      "prerequisite_concept_ids": [],
      "source_label": "extremal set theory",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_extremal-set-theory"
      ]
    },
    {
      "concept_id": "r012:concept:factored-advancement-operator-general-solution",
      "definition": "The general homogeneous solution is read from the roots and their multiplicities after factoring p(A), with complex roots requiring the corresponding complex-number setting or real conjugate combinations.",
      "prerequisite_concept_ids": [
        "r012:concept:distinct-root-recurrence-solution",
        "r012:concept:repeated-root-recurrence-solution"
      ],
      "source_label": "general solution from a factored advancement-operator polynomial",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rigorous_general",
        "r012:unit:auto:4411fbc2b5a9d67ef15e7dff",
        "r012:unit:s_recurrence_solving_homogeneous",
        "r012:unit:ex_recurrence_deg2",
        "r012:unit:ex_recurrence_ternary-strings-no-20-solved",
        "r012:unit:auto:6fb2d3d14bf9ef34219de62c",
        "r012:unit:ex_recurrence_deg2-repeated",
        "r012:unit:ex_recurrence_deg4-repeated",
        "r012:unit:rq-recurrence_solving-solve-plus-4",
        "r012:unit:rq-recurrence_solving-solve-plus-deg-two"
      ]
    },
    {
      "concept_id": "r012:concept:factorial",
      "definition": "For a nonnegative integer n, the product of the positive integers through n, with zero factorial equal to one.",
      "prerequisite_concept_ids": [
        "r012:concept:permutation"
      ],
      "source_label": "factorial",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_strings_permutations",
        "r012:unit:prop_strings_permutations",
        "r012:unit:s_genfunction_exponential",
        "r012:unit:s_ramsey_estimatesize"
      ]
    },
    {
      "concept_id": "r012:concept:failure",
      "definition": "The designated non-success outcome of a Bernoulli trial.",
      "prerequisite_concept_ids": [
        "r012:concept:bernoulli-trials"
      ],
      "source_label": "failure",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_bernoulli-trials"
      ]
    },
    {
      "concept_id": "r012:concept:fair-coin",
      "definition": "A two-outcome experiment assigning probability one half to each outcome.",
      "prerequisite_concept_ids": [
        "r012:concept:probability-space"
      ],
      "source_label": "fair coin",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_bernoulli-trials"
      ]
    },
    {
      "concept_id": "r012:concept:fair-game",
      "definition": "A game whose expected net payoff to each player is zero.",
      "prerequisite_concept_ids": [
        "r012:concept:probability",
        "r012:concept:expected-value"
      ],
      "source_label": "fair game",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:662e3bb0f4096cd83bffd676",
        "r012:unit:auto:60c6a1b068fc8ed42ca7593c",
        "r012:unit:auto:35a079f39425cb52d1e8033e"
      ]
    },
    {
      "concept_id": "r012:concept:falling-product-recurrence",
      "definition": "The recurrence P(p,k+1)=P(p,k)(p-k) for the falling product used in generalized binomial coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:generalized-binomial-coefficient",
        "r012:concept:nonnegative-integer"
      ],
      "source_label": "falling-product recurrence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:c03a554019cff7389d010e0a",
        "r012:unit:auto:19fe094123fad8db0f430437"
      ]
    },
    {
      "concept_id": "r012:concept:fibonacci-number",
      "definition": "An individual term of the Fibonacci sequence.",
      "prerequisite_concept_ids": [
        "r012:concept:fibonacci-sequence"
      ],
      "source_label": "Fibonacci number",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_intro_fib"
      ]
    },
    {
      "concept_id": "r012:concept:fibonacci-sequence",
      "definition": "The sequence 0, 1, 1, 2, 3, and so on, in which each later term is the sum of the preceding two terms.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence",
        "r012:concept:recurrence"
      ],
      "source_label": "Fibonacci sequence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_intro_fib",
        "r012:unit:tab_fib-ratios",
        "r012:unit:auto:a5fd615b1106d334b47d57d4",
        "r012:unit:ex_recurrence_binary-strings-no-11"
      ]
    },
    {
      "concept_id": "r012:concept:fibonacci-tiling-recurrence",
      "definition": "The recurrence obtained by partitioning 2-by-n domino tilings according to whether the right edge uses one vertical tile or two horizontal tiles.",
      "prerequisite_concept_ids": [
        "r012:concept:fibonacci-sequence",
        "r012:concept:recurrence",
        "r012:concept:checkerboard",
        "r012:concept:tile"
      ],
      "source_label": "Fibonacci recurrence for domino tilings",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:a5fd615b1106d334b47d57d4"
      ]
    },
    {
      "concept_id": "r012:concept:finite-cardinality",
      "definition": "For a finite set X, the unique n for which X is in bijection with [n], with the empty set assigned cardinality zero.",
      "prerequisite_concept_ids": [
        "r012:concept:finite-set",
        "r012:concept:bijection"
      ],
      "source_label": "cardinality",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_finite-sets"
      ]
    },
    {
      "concept_id": "r012:concept:finite-cartesian-product",
      "definition": "The set of n-tuples choosing one coordinate from each of n factor sets.",
      "prerequisite_concept_ids": [
        "r012:concept:cartesian-product",
        "r012:concept:tuple"
      ],
      "source_label": "finite Cartesian product",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_products"
      ]
    },
    {
      "concept_id": "r012:concept:finite-coloring",
      "definition": "An assignment of one of finitely many available colors to every object in a finite collection.",
      "prerequisite_concept_ids": [],
      "source_label": "finite coloring",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_square"
      ]
    },
    {
      "concept_id": "r012:concept:finite-decimal-expansion",
      "definition": "A decimal expansion with only finitely many nonzero digit positions.",
      "prerequisite_concept_ids": [
        "r012:concept:decimal-expansion"
      ],
      "source_label": "finite decimal expansion",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_complex"
      ]
    },
    {
      "concept_id": "r012:concept:finite-geometric-series",
      "definition": "The finite sum from j=0 to n of x^j, equal to (1-x^(n+1))/(1-x) when x is not 1.",
      "prerequisite_concept_ids": [
        "r012:concept:geometric-series"
      ],
      "source_label": "finite geometric series",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_intro",
        "r012:unit:eq_genfunction_finite-geom"
      ]
    },
    {
      "concept_id": "r012:concept:finite-injection-surjection-equivalence",
      "definition": "For nonempty finite X and finite Y, an injection X→Y exists exactly when a surjection Y→X exists.",
      "prerequisite_concept_ids": [
        "r012:concept:finite-set",
        "r012:concept:injection",
        "r012:concept:surjection"
      ],
      "source_label": "finite injection-surjection equivalence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_ZFC"
      ]
    },
    {
      "concept_id": "r012:concept:finite-set",
      "definition": "A set with finitely many elements.",
      "prerequisite_concept_ids": [],
      "source_label": "finite set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_intro",
        "r012:unit:s_background_finite-sets"
      ]
    },
    {
      "concept_id": "r012:concept:first-coordinate",
      "definition": "The first component of an ordered pair.",
      "prerequisite_concept_ids": [
        "r012:concept:ordered-pair"
      ],
      "source_label": "first coordinate",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_products"
      ]
    },
    {
      "concept_id": "r012:concept:first-decisive-event-probability",
      "definition": "For disjoint events with positive total probability, repeated independent sampling until A or B occurs yields win probability P(A)/(P(A)+P(B)).",
      "prerequisite_concept_ids": [
        "r012:concept:repeated-independent-sampling",
        "r012:concept:geometric-series",
        "r012:concept:disjoint-events"
      ],
      "source_label": "probability that A occurs before B under repeated sampling",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:9f5b75658465146534f073d6"
      ]
    },
    {
      "concept_id": "r012:concept:first-degree-advancement-operator-solution-space",
      "definition": "For (A-a)f=0, all scalar multiples of a^n are solutions.",
      "prerequisite_concept_ids": [
        "r012:concept:advancement-operator"
      ],
      "source_label": "solution space of a first-degree advancement-operator equation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:recurrence_PI_solve-deg-one"
      ]
    },
    {
      "concept_id": "r012:concept:first-fit-chain-partition",
      "definition": "A greedy assignment of poset elements to the first existing chain with which each new element is comparable.",
      "prerequisite_concept_ids": [
        "r012:concept:first-fit-coloring",
        "r012:concept:chain-partition",
        "r012:concept:poset-comparability"
      ],
      "source_label": "First Fit chain partition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_dilworth-intord"
      ]
    },
    {
      "concept_id": "r012:concept:first-fit-coloring",
      "definition": "A greedy coloring algorithm assigning each vertex the least available color in a chosen vertex order.",
      "prerequisite_concept_ids": [
        "r012:concept:proper-coloring",
        "r012:concept:algorithm"
      ],
      "source_label": "First Fit coloring",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_color",
        "r012:unit:thm_intgraphcol",
        "r012:unit:s_posets_dilworth-intord"
      ]
    },
    {
      "concept_id": "r012:concept:first-moment-method",
      "definition": "A probabilistic existence argument using an expectation bound and Markov's inequality or the fact that a nonnegative integer variable with expectation below one can vanish.",
      "prerequisite_concept_ids": [
        "r012:concept:expected-value",
        "r012:concept:probabilistic-method"
      ],
      "source_label": "first moment method",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_rnn",
        "r012:unit:thm_girth"
      ]
    },
    {
      "concept_id": "r012:concept:fishburn-theorem",
      "definition": "A poset is an interval order exactly when it contains no induced copy of the 2+2 poset.",
      "prerequisite_concept_ids": [
        "r012:concept:interval-order",
        "r012:concept:forbidden-subposet",
        "r012:concept:two-plus-two-poset"
      ],
      "source_label": "Fishburn's theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_fishburn"
      ]
    },
    {
      "concept_id": "r012:concept:fixed-bernoulli-outcome-string",
      "definition": "A particular length-n success/failure string with i successes has probability p^i(1-p)^(n-i).",
      "prerequisite_concept_ids": [
        "r012:concept:bernoulli-trials"
      ],
      "source_label": "probability of a fixed Bernoulli outcome string",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_bernoulli-trials"
      ]
    },
    {
      "concept_id": "r012:concept:fixed-coloring-under-transformation",
      "definition": "A coloring unchanged when a specified square symmetry acts on its vertices.",
      "prerequisite_concept_ids": [
        "r012:concept:square-vertex-coloring",
        "r012:concept:group-action"
      ],
      "source_label": "coloring fixed by a transformation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_square"
      ]
    },
    {
      "concept_id": "r012:concept:fixed-point",
      "definition": "An element i in the domain of a self-map sigma for which sigma(i)=i.",
      "prerequisite_concept_ids": [
        "r012:concept:function"
      ],
      "source_label": "fixed point",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:exa_inclusion-exclusion_prop-derange",
        "r012:unit:s_inclusion-exclusion_derangements",
        "r012:unit:auto:efc19c37945fe17ccd593b42",
        "r012:unit:inclusion-exclusion_PI_perm-prop"
      ]
    },
    {
      "concept_id": "r012:concept:fixed-set",
      "definition": "The set of objects left unchanged by a specified group element.",
      "prerequisite_concept_ids": [
        "r012:concept:group-action"
      ],
      "source_label": "fixed set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_burnside"
      ]
    },
    {
      "concept_id": "r012:concept:flow-conservation-law",
      "definition": "Flow entering each internal vertex equals flow leaving it, and total source outflow equals total sink inflow.",
      "prerequisite_concept_ids": [
        "r012:concept:network-flow"
      ],
      "source_label": "flow conservation laws",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_intro",
        "r012:unit:prop_networkflow_update"
      ]
    },
    {
      "concept_id": "r012:concept:flow-cut-capacity-bound",
      "definition": "Every feasible flow has value no greater than the capacity of any source-sink cut.",
      "prerequisite_concept_ids": [
        "r012:concept:flow-value",
        "r012:concept:cut-capacity"
      ],
      "source_label": "flow value is at most cut capacity",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_networkflow_flowleqcut"
      ]
    },
    {
      "concept_id": "r012:concept:flow-derived-chain-partition",
      "definition": "Trace full middle edges forward and backward to assemble the poset elements into chains.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-to-flow-network"
      ],
      "source_label": "flow-derived chain partition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_chain-partition",
        "r012:unit:s_flowapplications_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:flow-network",
      "definition": "An oriented graph with a distinguished source, a distinguished sink, and a nonnegative capacity on every directed edge.",
      "prerequisite_concept_ids": [
        "r012:concept:oriented-graph",
        "r012:concept:directed-edge"
      ],
      "source_label": "network",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_intro"
      ]
    },
    {
      "concept_id": "r012:concept:flow-value",
      "definition": "The total flow leaving the source, equivalently the total flow entering the sink.",
      "prerequisite_concept_ids": [
        "r012:concept:flow-conservation-law"
      ],
      "source_label": "value of a flow",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_intro",
        "r012:unit:s_networkflow_flows-cuts"
      ]
    },
    {
      "concept_id": "r012:concept:folder-distribution-model",
      "definition": "A stars-and-bars encoding in which folders represent distributed objects and selected gaps represent dividers between recipients.",
      "prerequisite_concept_ids": [
        "r012:concept:distribution",
        "r012:concept:binomial-coefficient"
      ],
      "source_label": "folder distribution model",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:328950a879727c218a6d3e20",
        "r012:unit:auto:76ca4cd132d1a847219afb0f"
      ]
    },
    {
      "concept_id": "r012:concept:forbidden-subposet",
      "definition": "A subposet whose presence prevents membership in a specified class of posets.",
      "prerequisite_concept_ids": [
        "r012:concept:subposet"
      ],
      "source_label": "forbidden subposet",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_fishburn"
      ]
    },
    {
      "concept_id": "r012:concept:forbidden-substring-recurrence",
      "definition": "A recurrence derived by partitioning restricted strings according to their final character or suffix.",
      "prerequisite_concept_ids": [
        "r012:concept:string",
        "r012:concept:recurrence",
        "r012:concept:substring",
        "r012:concept:recurrence-relation"
      ],
      "source_label": "recurrence for strings avoiding a forbidden substring",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_intro_strings",
        "r012:unit:ex_recurrence_binary-strings-no-11",
        "r012:unit:ex_recurrence_ternary-strings-no-20",
        "r012:unit:auto:be824cc6b96066d8d01042a9",
        "r012:unit:ex_recurrence_ternary-strings-no-20-solved",
        "r012:unit:eqn_recurrence_ternary"
      ]
    },
    {
      "concept_id": "r012:concept:ford-fulkerson-labeling-algorithm",
      "definition": "A breadth-first labeling procedure that repeatedly finds augmenting paths or certifies a minimum cut.",
      "prerequisite_concept_ids": [
        "r012:concept:augmenting-flow-update",
        "r012:concept:linear-order"
      ],
      "source_label": "Ford-Fulkerson labeling algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:alg_labeling",
        "r012:unit:s_networkflow_example"
      ]
    },
    {
      "concept_id": "r012:concept:forest",
      "definition": "An acyclic graph, possibly disconnected.",
      "prerequisite_concept_ids": [
        "r012:concept:acyclic-graph"
      ],
      "source_label": "forest",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro"
      ]
    },
    {
      "concept_id": "r012:concept:forest-online-color-lower-bound",
      "definition": "Builder can force n colors on a forest with at most 2^(n-1) revealed vertices.",
      "prerequisite_concept_ids": [
        "r012:concept:online-graph-coloring-game",
        "r012:concept:forest"
      ],
      "source_label": "forest online-color lower bound",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_olforest"
      ]
    },
    {
      "concept_id": "r012:concept:formal-power-series",
      "definition": "A power series treated algebraically through its coefficients without requiring analytic convergence.",
      "prerequisite_concept_ids": [
        "r012:concept:power-series"
      ],
      "source_label": "formal power series",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:5d06d4ea1ab81098c21c9be0",
        "r012:unit:s_genfunction_intro",
        "r012:unit:exam_genfunction_geom-series",
        "r012:unit:auto:0be40ee4fe111164419b75cb",
        "r012:unit:prop_genfunction-product",
        "r012:unit:s_genfunction_distributions",
        "r012:unit:s_genfunction_gen-bin-thm",
        "r012:unit:thm_newton-binomial"
      ]
    },
    {
      "concept_id": "r012:concept:four-color-theorem",
      "definition": "Every planar graph has a proper coloring using at most four colors.",
      "prerequisite_concept_ids": [
        "r012:concept:planar-graph",
        "r012:concept:proper-coloring"
      ],
      "source_label": "Four Color Theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_4ct",
        "r012:unit:fig_needs-four-colors"
      ]
    },
    {
      "concept_id": "r012:concept:fraction",
      "definition": "An expression with a numerator divided by a nonzero denominator.",
      "prerequisite_concept_ids": [],
      "source_label": "fraction",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:full-binary-tree",
      "definition": "A rooted tree in which every vertex has either zero children or exactly two children.",
      "prerequisite_concept_ids": [
        "r012:concept:rooted-tree"
      ],
      "source_label": "binary tree with zero or two children at each vertex",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots"
      ]
    },
    {
      "concept_id": "r012:concept:full-edge-selection-interpretation",
      "definition": "Edges carrying one unit of a unit-capacity integral flow encode selected combinatorial objects.",
      "prerequisite_concept_ids": [
        "r012:concept:unit-capacity-integral-flow"
      ],
      "source_label": "full-edge combinatorial selection",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_intro"
      ]
    },
    {
      "concept_id": "r012:concept:full-house",
      "definition": "A five-card poker hand with three cards of one rank and two of another rank.",
      "prerequisite_concept_ids": [
        "r012:concept:combination"
      ],
      "source_label": "full house",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:f7e40464a595ae094b2b7cdf"
      ]
    },
    {
      "concept_id": "r012:concept:full-house-probability",
      "definition": "The probability of choosing one rank for a triple and another rank for a pair in a five-card hand.",
      "prerequisite_concept_ids": [
        "r012:concept:combination",
        "r012:concept:equally-likely-outcomes"
      ],
      "source_label": "probability of a full house",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:f7e40464a595ae094b2b7cdf"
      ]
    },
    {
      "concept_id": "r012:concept:function",
      "definition": "A mapping that assigns exactly one codomain value to each domain element.",
      "prerequisite_concept_ids": [],
      "source_label": "function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_pigeonhole",
        "r012:unit:exa_inclusion-exclusion_prop-inject",
        "r012:unit:s_inclusion-exclusion_surjections",
        "r012:unit:inclusion-exclusion_PI_surjection",
        "r012:unit:inclusion-exclusion_PI_functions-count",
        "r012:unit:inclusion-exclusion_PI_function-property",
        "r012:unit:inclusion-exclusion_PI_perm-prop",
        "r012:unit:s_inclusion-exclusion_surjections_activity",
        "r012:unit:auto:12b6629772d99bdcaab15a9b",
        "r012:unit:ex_recurrence_diffeq",
        "r012:unit:ex_recurrence_adveq",
        "r012:unit:auto:ba2f054b693f6319b15736f2",
        "r012:unit:s_background_relations",
        "r012:unit:s_background_add"
      ]
    },
    {
      "concept_id": "r012:concept:function-as-relation",
      "definition": "A binary relation assigning exactly one codomain element to each domain element.",
      "prerequisite_concept_ids": [
        "r012:concept:binary-relation",
        "r012:concept:function"
      ],
      "source_label": "function as a binary relation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_relations",
        "r012:unit:exa_function"
      ]
    },
    {
      "concept_id": "r012:concept:function-composition",
      "definition": "The operation that applies one function to the output of another function.",
      "prerequisite_concept_ids": [],
      "source_label": "function composition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_square",
        "r012:unit:s_polya_perm-groups",
        "r012:unit:s_polya_burnside"
      ]
    },
    {
      "concept_id": "r012:concept:function-image",
      "definition": "The subset of a function's codomain consisting of values attained by at least one domain element.",
      "prerequisite_concept_ids": [
        "r012:concept:function"
      ],
      "source_label": "image of a function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:exa_inclusion-exclusion_prop-inject",
        "r012:unit:s_inclusion-exclusion_surjections",
        "r012:unit:s_inclusion-exclusion_surjections_activity",
        "r012:unit:def-image"
      ]
    },
    {
      "concept_id": "r012:concept:gale-ryser-theorem",
      "definition": "Row and column partitions R,C are realized by a zero-one matrix exactly when R^d dominates C.",
      "prerequisite_concept_ids": [
        "r012:concept:row-column-sum-strings",
        "r012:concept:dual-integer-partition",
        "r012:concept:partition-dominance-order"
      ],
      "source_label": "Gale–Ryser theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_zero-one-matrices"
      ]
    },
    {
      "concept_id": "r012:concept:general-ramsey-theorem",
      "definition": "For every finite coloring of fixed-size subsets, a sufficiently large ground set contains a prescribed-size subset whose fixed-size subsets all have one color.",
      "prerequisite_concept_ids": [
        "r012:concept:ramsey-property"
      ],
      "source_label": "general Ramsey theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_genramsey"
      ]
    },
    {
      "concept_id": "r012:concept:generalized-binomial-coefficient",
      "definition": "For real p and nonnegative integer k, the coefficient binom(p,k) is the falling product P(p,k) divided by k!.",
      "prerequisite_concept_ids": [
        "r012:concept:binomial-coefficient",
        "r012:concept:nonnegative-integer"
      ],
      "source_label": "generalized binomial coefficient",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_gen-bin-thm",
        "r012:unit:auto:8f3500f97b0ab7c55c94505a",
        "r012:unit:thm_newton-binomial",
        "r012:unit:s_genfunction_binom-app",
        "r012:unit:l_newbinom"
      ]
    },
    {
      "concept_id": "r012:concept:generalized-binomial-theorem",
      "definition": "The expansion of (1+x)^p using generalized binomial coefficients, interpreted formally or analytically within its convergence domain when the series does not terminate.",
      "prerequisite_concept_ids": [
        "r012:concept:generalized-binomial-coefficient",
        "r012:concept:formal-power-series"
      ],
      "source_label": "Newton's Binomial Theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_gen-bin-thm",
        "r012:unit:thm_newton-binomial",
        "r012:unit:s_genfunction_binom-app",
        "r012:unit:l_newbinom",
        "r012:unit:t_sqrt"
      ]
    },
    {
      "concept_id": "r012:concept:generating-function",
      "definition": "A formal power series encoding a sequence as coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:enumeration"
      ],
      "source_label": "generating function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:ch_genfunction",
        "r012:unit:auto:5d06d4ea1ab81098c21c9be0",
        "r012:unit:s_genfunction_intro",
        "r012:unit:exam_genfunction_geom-series",
        "r012:unit:auto:0be40ee4fe111164419b75cb",
        "r012:unit:prop_genfunction-product",
        "r012:unit:s_genfunction_distributions",
        "r012:unit:s_genfunction_gen-bin-thm",
        "r012:unit:s_genfunction_binom-app",
        "r012:unit:t_sqrt",
        "r012:unit:auto:77bb8e40ef7c0def33263edd",
        "r012:unit:s_genfunction_partitions-integer",
        "r012:unit:thm_partition",
        "r012:unit:auto:c1cbbffbb5bf258ea18be45d",
        "r012:unit:s_genfunction_exponential",
        "r012:unit:s_genfunction_exercises",
        "r012:unit:s_genfunction_PI",
        "r012:unit:ch_recurrence",
        "r012:unit:auto:b2a4979434434bc7233ca327"
      ]
    },
    {
      "concept_id": "r012:concept:generating-function-coefficient-shift",
      "definition": "Multiplication of a generating function by x^k shifts its coefficients by k indices, allowing recurrence terms to be aligned at one power x^n.",
      "prerequisite_concept_ids": [
        "r012:concept:generating-function",
        "r012:concept:sequence"
      ],
      "source_label": "coefficient shift by multiplying a generating function by a monomial",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_genfunction",
        "r012:unit:ex_recurrence_gf-homog",
        "r012:unit:ex_recurrence_gf-nonhomog"
      ]
    },
    {
      "concept_id": "r012:concept:generating-function-distribution-model",
      "definition": "A coefficient model that assigns a generating-function factor to each recipient or object type and multiplies the factors to encode all admissible distributions.",
      "prerequisite_concept_ids": [
        "r012:concept:generating-function",
        "r012:concept:distribution",
        "r012:concept:power-series-product"
      ],
      "source_label": "generating-function model for distributions",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_distributions",
        "r012:unit:exa_genfunction_apples",
        "r012:unit:exa_genfunction_fruit",
        "r012:unit:auto:2d043fada756b0e678fbcfa4",
        "r012:unit:exa_genfunction_partial-fracs",
        "r012:unit:auto:692d3d5206064b390fb35ace",
        "r012:unit:exa_genfunction_multisets",
        "r012:unit:auto:d7c45bbaac6cda937a07c30e",
        "r012:unit:rqs-genfunction_distributions",
        "r012:unit:genfunction_distributions_rq-constant_term",
        "r012:unit:genfunction_distributions_rq-coins",
        "r012:unit:auto:e1321354951ba5fcec2ae15c",
        "r012:unit:auto:ad5800950b29d7f51c43a73e",
        "r012:unit:ex_genfunction_ineq-clean",
        "r012:unit:auto:6b0d982902d4e6cfc0dfed45",
        "r012:unit:auto:318098a808461c4b431eaeec",
        "r012:unit:auto:9da8ebe78f63c221b5b6bc64",
        "r012:unit:auto:8def6d29b55112ab987c47ed",
        "r012:unit:ex_genfunction_ineq-messy",
        "r012:unit:genfunction_PI_apples-one",
        "r012:unit:genfunction_PI_apples-five",
        "r012:unit:genfunction_PI_apples-oranges-bananas",
        "r012:unit:genfunction_PI_polynomial"
      ]
    },
    {
      "concept_id": "r012:concept:generating-function-exercise-synthesis",
      "definition": "Integrated practice translating sequences and combinatorial restrictions into generating functions and extracting the required coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:generating-function"
      ],
      "source_label": "generating-function exercise synthesis",
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      "unit_ids": [
        "r012:unit:s_genfunction_exercises",
        "r012:unit:auto:e3dfb8524ffbb34b5062db90"
      ]
    },
    {
      "concept_id": "r012:concept:generating-function-recurrence-method",
      "definition": "A method that converts a recurrence and its initial conditions into an algebraic equation for a generating function, then extracts a closed form from its coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:linear-recurrence-equation",
        "r012:concept:ordinary-generating-function",
        "r012:concept:generating-function-coefficient-shift",
        "r012:concept:partial-fraction-coefficient-extraction",
        "r012:concept:initial-condition"
      ],
      "source_label": "generating-function method for recurrence equations",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_genfunction",
        "r012:unit:ex_recurrence_gf-homog",
        "r012:unit:ex_recurrence_gf-nonhomog"
      ]
    },
    {
      "concept_id": "r012:concept:geometric-series",
      "definition": "A finite or infinite sum whose successive terms have a constant ratio; the introductory infinite case is the sum from n=0 to infinity of x^n.",
      "prerequisite_concept_ids": [
        "r012:concept:power-series"
      ],
      "source_label": "geometric series",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_intro",
        "r012:unit:exam_genfunction_geom-series",
        "r012:unit:eq_genfunction_finite-geom"
      ]
    },
    {
      "concept_id": "r012:concept:geometry",
      "definition": "The study of spatial structures, incidence, distance, and shape.",
      "prerequisite_concept_ids": [
        "r012:concept:combinatorics"
      ],
      "source_label": "geometry",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_geom"
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    },
    {
      "concept_id": "r012:concept:graduate-fellowship",
      "definition": "Competitive funding supporting postgraduate study.",
      "prerequisite_concept_ids": [],
      "source_label": "graduate fellowship",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:graph",
      "definition": "A discrete structure consisting of vertices and edges.",
      "prerequisite_concept_ids": [
        "r012:concept:discrete-structures"
      ],
      "source_label": "graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:s_intro_graph",
        "r012:unit:fig_graphdata",
        "r012:unit:fig_connectedgraph",
        "r012:unit:ex_radiostations",
        "r012:unit:auto:4f427a0d8cd35dd9d5f9a181",
        "r012:unit:ch_graphs"
      ]
    },
    {
      "concept_id": "r012:concept:graph-algorithm",
      "definition": "An algorithm for a computational problem whose input or state is a graph.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:algorithm"
      ],
      "source_label": "graph algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_graphalgorithms"
      ]
    },
    {
      "concept_id": "r012:concept:graph-circuit",
      "definition": "A closed trail, beginning and ending at the same vertex without repeating an edge.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-walk",
        "r012:concept:cycle"
      ],
      "source_label": "circuit",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_eulerham"
      ]
    },
    {
      "concept_id": "r012:concept:graph-coloring",
      "definition": "Assignment of labels to vertices so that adjacent vertices receive different labels.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:adjacency"
      ],
      "source_label": "frequency assignment as graph coloring",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ex_radiostations",
        "r012:unit:fig_radiostations"
      ]
    },
    {
      "concept_id": "r012:concept:graph-connectivity",
      "definition": "A graph is connected when every pair of vertices is joined by a path.",
      "prerequisite_concept_ids": [
        "r012:concept:path"
      ],
      "source_label": "connected graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_graph",
        "r012:unit:fig_connectedgraph"
      ]
    },
    {
      "concept_id": "r012:concept:graph-face",
      "definition": "A connected region of the plane complementary to a planar drawing, including the unbounded region.",
      "prerequisite_concept_ids": [
        "r012:concept:planar-drawing"
      ],
      "source_label": "face",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_planar"
      ]
    },
    {
      "concept_id": "r012:concept:graph-girth",
      "definition": "The length of a shortest cycle in a graph.",
      "prerequisite_concept_ids": [
        "r012:concept:cycle",
        "r012:concept:graph"
      ],
      "source_label": "girth",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_exercises",
        "r012:unit:s_ramsey_girth",
        "r012:unit:thm_girth"
      ]
    },
    {
      "concept_id": "r012:concept:graph-homeomorphism",
      "definition": "Graphs obtainable from isomorphic graphs by sequences of elementary subdivisions.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-isomorphism",
        "r012:concept:elementary-subdivision"
      ],
      "source_label": "homeomorphic graphs",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_planar",
        "r012:unit:thm_kuratowski"
      ]
    },
    {
      "concept_id": "r012:concept:graph-incidence",
      "definition": "The relation between a vertex and an edge having that vertex as an endpoint.",
      "prerequisite_concept_ids": [
        "r012:concept:vertex",
        "r012:concept:edge"
      ],
      "source_label": "incidence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro",
        "r012:unit:prop_networkflow_update",
        "r012:unit:alg_labeling",
        "r012:unit:ex_networkflow_update"
      ]
    },
    {
      "concept_id": "r012:concept:graph-isomorphism",
      "definition": "A bijection between vertex sets that preserves adjacency in both directions.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:adjacency",
        "r012:concept:bijection"
      ],
      "source_label": "graph isomorphism",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro",
        "r012:unit:fig_isomorphic",
        "r012:unit:fig_nonisomorphic"
      ]
    },
    {
      "concept_id": "r012:concept:graph-loop",
      "definition": "An edge whose two endpoints are the same vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "loop",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_multigraphs"
      ]
    },
    {
      "concept_id": "r012:concept:graph-neighbor",
      "definition": "A vertex adjacent to a given vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:adjacency"
      ],
      "source_label": "neighbor",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro",
        "r012:unit:alg_labeling",
        "r012:unit:s_networkflow_example",
        "r012:unit:s_networkflow_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:graph-ramsey-theorem",
      "definition": "Every sufficiently large graph contains a clique of a prescribed size or an independent set of a prescribed size.",
      "prerequisite_concept_ids": [
        "r012:concept:ramsey-property"
      ],
      "source_label": "Ramsey's theorem for graphs",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_graphramsey"
      ]
    },
    {
      "concept_id": "r012:concept:graph-walk",
      "definition": "A vertex sequence in which every consecutive pair is adjacent.",
      "prerequisite_concept_ids": [
        "r012:concept:adjacency"
      ],
      "source_label": "walk",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro"
      ]
    },
    {
      "concept_id": "r012:concept:greatest-common-divisor",
      "definition": "The greatest positive integer dividing each of two positive integers.",
      "prerequisite_concept_ids": [
        "r012:concept:divisibility"
      ],
      "source_label": "greatest common divisor",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_gcd",
        "r012:unit:thm_euclideanalg",
        "r012:unit:s_inclusion-exclusion_euler-phi"
      ]
    },
    {
      "concept_id": "r012:concept:greedy-algorithm",
      "definition": "An algorithm that repeatedly makes a locally optimal admissible choice.",
      "prerequisite_concept_ids": [
        "r012:concept:algorithm",
        "r012:concept:algorithms-optimization"
      ],
      "source_label": "greedy algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_min-wt-span"
      ]
    },
    {
      "concept_id": "r012:concept:ground-set",
      "definition": "The underlying set on which a relation or combinatorial structure is defined.",
      "prerequisite_concept_ids": [],
      "source_label": "ground set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro"
      ]
    },
    {
      "concept_id": "r012:concept:group",
      "definition": "A set with an associative binary operation, an identity element, and an inverse for every element.",
      "prerequisite_concept_ids": [],
      "source_label": "group",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_burnside",
        "r012:unit:s_polya_apps",
        "r012:unit:s_polya_perm-groups"
      ]
    },
    {
      "concept_id": "r012:concept:group-action",
      "definition": "A rule by which each group element transforms the objects in a set compatibly with group composition.",
      "prerequisite_concept_ids": [
        "r012:concept:group",
        "r012:concept:function-composition"
      ],
      "source_label": "group action",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_burnside"
      ]
    },
    {
      "concept_id": "r012:concept:hall-neighborhood-condition",
      "definition": "Every subset of the first bipartition class has at least as many neighbors as vertices.",
      "prerequisite_concept_ids": [
        "r012:concept:bipartite-matching"
      ],
      "source_label": "Hall neighborhood condition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_flowapplications_hall"
      ]
    },
    {
      "concept_id": "r012:concept:hall-theorem",
      "definition": "A bipartite graph has a matching saturating its first part exactly when Hall's neighborhood condition holds.",
      "prerequisite_concept_ids": [
        "r012:concept:hall-neighborhood-condition",
        "r012:concept:matching-saturation"
      ],
      "source_label": "Hall's theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_flowapplications_hall"
      ]
    },
    {
      "concept_id": "r012:concept:hamiltonian-cycle",
      "definition": "A cycle containing every vertex of a graph exactly once before returning to its start.",
      "prerequisite_concept_ids": [
        "r012:concept:cycle",
        "r012:concept:vertex"
      ],
      "source_label": "hamiltonian cycle",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_eulerham",
        "r012:unit:fig_eulham",
        "r012:unit:fig_petersen"
      ]
    },
    {
      "concept_id": "r012:concept:hamiltonian-graph",
      "definition": "A graph possessing a Hamiltonian cycle.",
      "prerequisite_concept_ids": [
        "r012:concept:hamiltonian-cycle"
      ],
      "source_label": "hamiltonian graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_eulerham",
        "r012:unit:fig_eulham",
        "r012:unit:fig_petersen"
      ]
    },
    {
      "concept_id": "r012:concept:hasse-diagram",
      "definition": "A drawing of a finite poset using its cover relations, with larger elements placed above smaller ones.",
      "prerequisite_concept_ids": [
        "r012:concept:cover-relation",
        "r012:concept:cover-graph"
      ],
      "source_label": "Hasse diagram",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:fig_covergraphs",
        "r012:unit:fig_17ptposet"
      ]
    },
    {
      "concept_id": "r012:concept:hat-check-problem",
      "definition": "A story model for counting or measuring the probability of assigning hats to people so that specified people do or do not receive their own hats.",
      "prerequisite_concept_ids": [
        "r012:concept:derangement"
      ],
      "source_label": "Hat Check problem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_inclusion-exclusion_derangements",
        "r012:unit:auto:0faa5a1d42e8503171d0a48a"
      ]
    },
    {
      "concept_id": "r012:concept:heap-priority-structure",
      "definition": "A priority structure supporting efficient repeated selection of a least-weight candidate edge.",
      "prerequisite_concept_ids": [
        "r012:concept:prim-algorithm"
      ],
      "source_label": "heap",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_min-wt-span"
      ]
    },
    {
      "concept_id": "r012:concept:homogeneous-linear-recurrence",
      "definition": "A linear recurrence equation whose forcing function is identically zero.",
      "prerequisite_concept_ids": [
        "r012:concept:linear-recurrence-equation"
      ],
      "source_label": "homogeneous linear recurrence equation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_linear",
        "r012:unit:rq-recurrence_linear-matching",
        "r012:unit:s_recurrence_solving_homogeneous",
        "r012:unit:ex_recurrence_deg2",
        "r012:unit:eqn_recurrence_deg2",
        "r012:unit:ex_recurrence_ternary-strings-no-20-solved",
        "r012:unit:auto:6fb2d3d14bf9ef34219de62c",
        "r012:unit:ex_recurrence_deg2-repeated",
        "r012:unit:ex_recurrence_deg4-repeated",
        "r012:unit:rq-recurrence_solving-solve-plus-4",
        "r012:unit:rq-recurrence_solving-solve-plus-deg-two"
      ]
    },
    {
      "concept_id": "r012:concept:homogeneous-recurrence-classification",
      "definition": "Recognition of linear recurrence equations whose forcing term is identically zero.",
      "prerequisite_concept_ids": [
        "r012:concept:homogeneous-linear-recurrence"
      ],
      "source_label": "classification of homogeneous recurrences",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:recurrence_PI_homogeneous"
      ]
    },
    {
      "concept_id": "r012:concept:homogeneous-recurrence-solution-space",
      "definition": "For a degree-k advancement-operator polynomial with nonzero leading and constant coefficients, the solutions of p(A)f=0 form a k-dimensional vector subspace.",
      "prerequisite_concept_ids": [
        "r012:concept:linear-recurrence-equation",
        "r012:concept:advancement-operator-polynomial",
        "r012:concept:vector-subspace",
        "r012:concept:vector-space-basis-and-dimension"
      ],
      "source_label": "solution space of a homogeneous linear recurrence equation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rigorous_principal",
        "r012:unit:thm_advance",
        "r012:unit:s_recurrence_solving_homogeneous",
        "r012:unit:ex_recurrence_deg2"
      ]
    },
    {
      "concept_id": "r012:concept:identity-transformation",
      "definition": "A transformation that leaves every object in its domain unchanged.",
      "prerequisite_concept_ids": [
        "r012:concept:group-action"
      ],
      "source_label": "identity transformation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_square"
      ]
    },
    {
      "concept_id": "r012:concept:imaginary-unit",
      "definition": "The complex number i=(0,1), whose square is -1.",
      "prerequisite_concept_ids": [
        "r012:concept:complex-number-system"
      ],
      "source_label": "imaginary unit",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_complex"
      ]
    },
    {
      "concept_id": "r012:concept:inclusion-exclusion",
      "definition": "A counting principle that alternates intersections to correct overlap.",
      "prerequisite_concept_ids": [
        "r012:concept:enumeration"
      ],
      "source_label": "inclusion/exclusion",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:ch_inclusion-exclusion",
        "r012:unit:s_inclusion-exclusion_intro",
        "r012:unit:exa_inclusion-exclusion_students",
        "r012:unit:exa_inclusion-exclusion_int-solns",
        "r012:unit:exa_inclusion-exclusion_prop-inject",
        "r012:unit:exa_inclusion-exclusion_prop-derange",
        "r012:unit:exa_inclusion-exclusion_prop-divis",
        "r012:unit:s_inclusion-exclusion_statement",
        "r012:unit:thm_inclusion-exclusion",
        "r012:unit:eq_inclusion-exclusion",
        "r012:unit:s_inclusion-exclusion_surjections",
        "r012:unit:auto:d82b928b4ab1bfb15c849fb5",
        "r012:unit:s_inclusion-exclusion_derangements",
        "r012:unit:auto:0ccd82df017d6432c7a435f0",
        "r012:unit:s_inclusion-exclusion_euler-phi",
        "r012:unit:thm_eulerphi",
        "r012:unit:auto:40c708c69ade17788d6a5947",
        "r012:unit:s_inclusion-exclusion_PI",
        "r012:unit:inclusion-exclusion_PI_IE-sum-terms",
        "r012:unit:s_inclusion-exclusion_surjections_activity",
        "r012:unit:s_genfunction_exponential"
      ]
    },
    {
      "concept_id": "r012:concept:inclusion-exclusion-property",
      "definition": "An unambiguous predicate P_i on a set X such that each element of X either satisfies P_i or does not.",
      "prerequisite_concept_ids": [
        "r012:concept:enumeration"
      ],
      "source_label": "property in an inclusion-exclusion family",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_inclusion-exclusion_intro",
        "r012:unit:s_inclusion-exclusion_statement",
        "r012:unit:thm_inclusion-exclusion",
        "r012:unit:s_inclusion-exclusion_surjections",
        "r012:unit:auto:0436226a7a3aec223fbb66d8",
        "r012:unit:inclusion-exclusion_PI_function-property",
        "r012:unit:inclusion-exclusion_PI_perm-prop",
        "r012:unit:s_inclusion-exclusion_surjections_activity",
        "r012:unit:inclusion-exclusion_activity_function-property"
      ]
    },
    {
      "concept_id": "r012:concept:inclusive-exclusive-or",
      "definition": "Inclusive or allows one or both alternatives, whereas exclusive or allows exactly one.",
      "prerequisite_concept_ids": [],
      "source_label": "inclusive and exclusive or",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_int-union"
      ]
    },
    {
      "concept_id": "r012:concept:incomparability",
      "definition": "The condition that neither of two elements precedes the other in a partial order.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order"
      ],
      "source_label": "incomparability",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_extremal-set-theory",
        "r012:unit:s_kitchensink_online"
      ]
    },
    {
      "concept_id": "r012:concept:incomparability-graph",
      "definition": "A graph joining exactly the distinct incomparable pairs of a poset.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:poset-comparability"
      ],
      "source_label": "incomparability graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:increasing-subsequence",
      "definition": "A subsequence whose terms increase in their inherited order.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence"
      ],
      "source_label": "increasing subsequence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_ErdosSzekeres",
        "r012:unit:s_basics_exact"
      ]
    },
    {
      "concept_id": "r012:concept:independent-events",
      "definition": "Events A and B are independent when P(A intersect B)=P(A)P(B).",
      "prerequisite_concept_ids": [
        "r012:concept:event",
        "r012:concept:conditional-probability"
      ],
      "source_label": "independent events",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:e890493d9ce5282dd02dd98c",
        "r012:unit:s_kitchensink_lovasz-local"
      ]
    },
    {
      "concept_id": "r012:concept:independent-graph",
      "definition": "A graph in which no pair of distinct vertices is adjacent.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:adjacency"
      ],
      "source_label": "independent graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro"
      ]
    },
    {
      "concept_id": "r012:concept:independent-set",
      "definition": "A set of vertices no two of which are adjacent.",
      "prerequisite_concept_ids": [
        "r012:concept:adjacency"
      ],
      "source_label": "independent set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_graph",
        "r012:unit:auto:21546ae1bdf04f7552481516",
        "r012:unit:s_probmeth_graph-ramsey",
        "r012:unit:s_ramsey_probability",
        "r012:unit:s_ramsey_girth",
        "r012:unit:s_ramsey_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:independent-set-bad-event",
      "definition": "A chosen n-vertex set spans no edges in the random graph.",
      "prerequisite_concept_ids": [
        "r012:concept:random-graph",
        "r012:concept:independent-set"
      ],
      "source_label": "independent-set bad event",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_applying-local-lemma"
      ]
    },
    {
      "concept_id": "r012:concept:induced-subgraph",
      "definition": "The subgraph on a selected vertex set containing every original edge between selected vertices.",
      "prerequisite_concept_ids": [
        "r012:concept:subgraph"
      ],
      "source_label": "induced subgraph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro",
        "r012:unit:fig_subgraphs",
        "r012:unit:rq-graphs_intro_subgraph",
        "r012:unit:s_probmeth_graph-ramsey"
      ]
    },
    {
      "concept_id": "r012:concept:induction-hypothesis",
      "definition": "The earlier instance or instances assumed within the inductive step of a proof.",
      "prerequisite_concept_ids": [
        "r012:concept:mathematical-induction"
      ],
      "source_label": "induction hypothesis",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_strong-induction",
        "r012:unit:auto:157db7e274f439b81e0dec9b"
      ]
    },
    {
      "concept_id": "r012:concept:induction-step",
      "definition": "The implication that propagates established or assumed instances to the next instance in an inductive proof.",
      "prerequisite_concept_ids": [
        "r012:concept:mathematical-induction",
        "r012:concept:induction-hypothesis"
      ],
      "source_label": "induction step",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_strong-induction"
      ]
    },
    {
      "concept_id": "r012:concept:inductive-definition",
      "definition": "A definition that begins with specified initial objects and includes further objects whenever stated inductive rules apply.",
      "prerequisite_concept_ids": [
        "r012:concept:recursion"
      ],
      "source_label": "inductive definition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_inductdefs"
      ]
    },
    {
      "concept_id": "r012:concept:industrial-optimization",
      "definition": "Using optimization to improve operational and manufacturing decisions.",
      "prerequisite_concept_ids": [],
      "source_label": "industrial optimization",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:inequivalent-coloring",
      "definition": "A coloring counted as distinct after colorings related by an allowed group action are identified.",
      "prerequisite_concept_ids": [
        "r012:concept:coloring-equivalence-under-action"
      ],
      "source_label": "inequivalent coloring",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_polya"
      ]
    },
    {
      "concept_id": "r012:concept:infinite-probability-space",
      "definition": "A probability space whose sample space has infinitely many outcomes.",
      "prerequisite_concept_ids": [
        "r012:concept:probability-space",
        "r012:concept:sample-space"
      ],
      "source_label": "probability space with infinitely many outcomes",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_infinite-outcomes"
      ]
    },
    {
      "concept_id": "r012:concept:infinite-series",
      "definition": "A limit of finite partial sums of a sequence.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence"
      ],
      "source_label": "infinite series",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_infinite-outcomes"
      ]
    },
    {
      "concept_id": "r012:concept:infinite-set",
      "definition": "A set that is not finite.",
      "prerequisite_concept_ids": [
        "r012:concept:finite-set"
      ],
      "source_label": "infinite set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_finite-sets"
      ]
    },
    {
      "concept_id": "r012:concept:initial-condition",
      "definition": "A specified value of a function or sequence at an initial index that selects a particular solution from a family satisfying an equation.",
      "prerequisite_concept_ids": [
        "r012:concept:function",
        "r012:concept:sequence",
        "r012:concept:recurrence-relation"
      ],
      "source_label": "initial condition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ex_recurrence_diffeq",
        "r012:unit:auto:27087d0ded854684444635f4",
        "r012:unit:ex_recurrence_adveq",
        "r012:unit:auto:03810a7758a5b5bb714c9db1",
        "r012:unit:ex_recurrence_gf-homog",
        "r012:unit:ex_recurrence_gf-nonhomog",
        "r012:unit:ex_recurrence_ternary-strings-no-20-solved",
        "r012:unit:ex_recurrence_deg4-repeated",
        "r012:unit:auto:2b9501b6517e77e868e24689",
        "r012:unit:ex_recurrence_lines-solved",
        "r012:unit:rq-recurrence_solving-solve-plus-4"
      ]
    },
    {
      "concept_id": "r012:concept:initial-public-offering",
      "definition": "A company's first public sale of shares.",
      "prerequisite_concept_ids": [
        "r012:concept:technology-entrepreneurship"
      ],
      "source_label": "initial public offering",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:initial-segment-notation",
      "definition": "Standard finite-set notations for the first n positive or nonnegative integers.",
      "prerequisite_concept_ids": [
        "r012:concept:positive-integer",
        "r012:concept:nonnegative-integer"
      ],
      "source_label": "[n] and bold n",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_int-union"
      ]
    },
    {
      "concept_id": "r012:concept:initial-value-constant-determination",
      "definition": "Substitute the specified initial values into a parametric general solution and solve the resulting finite system for its constants.",
      "prerequisite_concept_ids": [
        "r012:concept:linear-recurrence-equation",
        "r012:concept:initial-condition"
      ],
      "source_label": "determining constants from initial values",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ex_recurrence_ternary-strings-no-20-solved",
        "r012:unit:ex_recurrence_deg4-repeated",
        "r012:unit:auto:2b9501b6517e77e868e24689",
        "r012:unit:ex_recurrence_lines-solved",
        "r012:unit:rq-recurrence_solving-solve-plus-4"
      ]
    },
    {
      "concept_id": "r012:concept:injection",
      "definition": "A function that maps distinct domain elements to distinct codomain elements.",
      "prerequisite_concept_ids": [
        "r012:concept:function"
      ],
      "source_label": "injective function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_pigeonhole",
        "r012:unit:s_background_relations",
        "r012:unit:exe_sb",
        "r012:unit:s_background_formal-num-sys"
      ]
    },
    {
      "concept_id": "r012:concept:integer",
      "definition": "A member of the number system containing the nonnegative integers and their additive inverses.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-construction"
      ],
      "source_label": "integer",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_integers",
        "r012:unit:s_background_prop-integers",
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:integer-addition",
      "definition": "Addition of integer classes by componentwise addition of ordered-pair representatives.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-construction",
        "r012:concept:well-defined-operation"
      ],
      "source_label": "integer addition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_prop-integers"
      ]
    },
    {
      "concept_id": "r012:concept:integer-construction",
      "definition": "An integer is an equivalence class of ordered pairs of nonnegative integers under difference equality.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-pair-equivalence",
        "r012:concept:equivalence-class"
      ],
      "source_label": "integers as equivalence classes",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_integers"
      ]
    },
    {
      "concept_id": "r012:concept:integer-division",
      "definition": "For positive integers m and n, the unique representation m=qn+r with quotient q and remainder satisfying 0 <= r < n.",
      "prerequisite_concept_ids": [
        "r012:concept:positive-integer"
      ],
      "source_label": "Division Theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_division"
      ]
    },
    {
      "concept_id": "r012:concept:integer-endpoint",
      "definition": "An interval endpoint whose coordinate is an integer.",
      "prerequisite_concept_ids": [
        "r012:concept:interval-endpoint"
      ],
      "source_label": "integer endpoint",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_intord-minrep"
      ]
    },
    {
      "concept_id": "r012:concept:integer-exponentiation",
      "definition": "Recursive exponentiation with x^0=1 and x^(k+1)=x x^k.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-multiplication",
        "r012:concept:mathematical-induction"
      ],
      "source_label": "nonnegative integer powers",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_prop-integers"
      ]
    },
    {
      "concept_id": "r012:concept:integer-exponents-on-rationals",
      "definition": "Nonnegative powers are recursive and negative powers use reciprocals.",
      "prerequisite_concept_ids": [
        "r012:concept:rational-arithmetic",
        "r012:concept:multiplicative-inverse",
        "r012:concept:integer-exponentiation"
      ],
      "source_label": "integer exponents of rational numbers",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:integer-maximum-flow-integrality",
      "definition": "If every edge capacity is integral, some maximum flow is integral on every edge.",
      "prerequisite_concept_ids": [
        "r012:concept:maximum-flow"
      ],
      "source_label": "integral maximum-flow theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_intro"
      ]
    },
    {
      "concept_id": "r012:concept:integer-multiplication",
      "definition": "Multiplication of pair classes using (a,b)(c,d)=(ac+bd,ad+bc).",
      "prerequisite_concept_ids": [
        "r012:concept:integer-construction",
        "r012:concept:well-defined-operation"
      ],
      "source_label": "integer multiplication",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_prop-integers"
      ]
    },
    {
      "concept_id": "r012:concept:integer-pair-equivalence",
      "definition": "Pairs (a,b) and (c,d) of nonnegative integers are equivalent when a+d=b+c.",
      "prerequisite_concept_ids": [
        "r012:concept:ordered-pair",
        "r012:concept:equivalence-relation",
        "r012:concept:nonnegative-integer"
      ],
      "source_label": "ordered-pair equivalence for integers",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_integers"
      ]
    },
    {
      "concept_id": "r012:concept:integer-pair-equivalence-proof",
      "definition": "Reflexivity, symmetry, and transitivity establish that the pair relation partitions the pair set.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-pair-equivalence"
      ],
      "source_label": "equivalence proof for integer pairs",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_integers"
      ]
    },
    {
      "concept_id": "r012:concept:integer-partition",
      "definition": "A representation of a positive integer as an unordered sum of positive integers.",
      "prerequisite_concept_ids": [
        "r012:concept:positive-integer",
        "r012:concept:partition"
      ],
      "source_label": "integer partition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_number",
        "r012:unit:fig_intro_partsof8",
        "r012:unit:s_genfunction_partitions-integer",
        "r012:unit:fig_genfunction_partsof8",
        "r012:unit:s_genfunction_discussion",
        "r012:unit:auto:c53a9727c6ac71ed663831ee",
        "r012:unit:auto:e0f50e92137238f006185b9f",
        "r012:unit:auto:5a5a5f490053509f506e2e65",
        "r012:unit:auto:fce61924f5d5515db0dda1a7"
      ]
    },
    {
      "concept_id": "r012:concept:integer-total-order",
      "definition": "The order induced on pair classes by comparing the corresponding cross sums.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-construction",
        "r012:concept:total-order"
      ],
      "source_label": "total order on the integers",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_prop-integers"
      ]
    },
    {
      "concept_id": "r012:concept:integer-zero",
      "definition": "The additive identity in the integer number system.",
      "prerequisite_concept_ids": [
        "r012:concept:integer"
      ],
      "source_label": "integer zero",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_prop-integers"
      ]
    },
    {
      "concept_id": "r012:concept:integral-maximum-flow",
      "definition": "For integral capacities, a maximum flow exists whose value on every edge is an integer.",
      "prerequisite_concept_ids": [
        "r012:concept:ford-fulkerson-labeling-algorithm"
      ],
      "source_label": "integral maximum flow",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_integer-programming"
      ]
    },
    {
      "concept_id": "r012:concept:intersecting-set-family",
      "definition": "A family in which every two members have nonempty intersection.",
      "prerequisite_concept_ids": [
        "r012:concept:set-family"
      ],
      "source_label": "intersecting family",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:exa_intersecting",
        "r012:unit:s_kitchensink_extremal-set-theory"
      ]
    },
    {
      "concept_id": "r012:concept:intersection-graph",
      "definition": "A graph representing a family of sets, with adjacency exactly when two represented sets intersect.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "intersection graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_color",
        "r012:unit:fig_graphs_interval-graph"
      ]
    },
    {
      "concept_id": "r012:concept:interval-endpoint",
      "definition": "The left or right boundary value of an interval.",
      "prerequisite_concept_ids": [
        "r012:concept:closed-interval"
      ],
      "source_label": "interval endpoint",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intervalorder"
      ]
    },
    {
      "concept_id": "r012:concept:interval-graph",
      "definition": "The intersection graph of a family of intervals on a line.",
      "prerequisite_concept_ids": [
        "r012:concept:intersection-graph"
      ],
      "source_label": "interval graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:fig_graphs_interval-graph",
        "r012:unit:thm_intgraphcol",
        "r012:unit:s_posets_dilworth-intord"
      ]
    },
    {
      "concept_id": "r012:concept:interval-order",
      "definition": "A poset represented by real intervals, with x<y exactly when the interval for x lies completely to the left of the interval for y.",
      "prerequisite_concept_ids": [
        "r012:concept:poset",
        "r012:concept:closed-interval"
      ],
      "source_label": "interval order",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intervalorder",
        "r012:unit:thm_fishburn"
      ]
    },
    {
      "concept_id": "r012:concept:interval-order-width-algorithm",
      "definition": "An optimal width and chain-partition procedure obtained from perfect coloring of the incomparability interval graph.",
      "prerequisite_concept_ids": [
        "r012:concept:interval-order",
        "r012:concept:perfect-graph",
        "r012:concept:first-fit-chain-partition",
        "r012:concept:poset-width"
      ],
      "source_label": "interval-order width algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_dilworth-intord"
      ]
    },
    {
      "concept_id": "r012:concept:interval-representation",
      "definition": "An assignment of a closed real interval to each poset element that realizes its order relation.",
      "prerequisite_concept_ids": [
        "r012:concept:interval-order",
        "r012:concept:closed-interval"
      ],
      "source_label": "interval representation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intervalorder",
        "r012:unit:fig_6ptintorder"
      ]
    },
    {
      "concept_id": "r012:concept:inventory-substitution",
      "definition": "Replacing each cycle variable x_i by the sum of i-th powers of color variables.",
      "prerequisite_concept_ids": [
        "r012:concept:cycle-index",
        "r012:concept:generating-function"
      ],
      "source_label": "inventory substitution",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_polya"
      ]
    },
    {
      "concept_id": "r012:concept:inverse-transformation",
      "definition": "A transformation that reverses the effect of another transformation.",
      "prerequisite_concept_ids": [
        "r012:concept:permutation",
        "r012:concept:function-composition"
      ],
      "source_label": "inverse transformation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_square"
      ]
    },
    {
      "concept_id": "r012:concept:irrational-number",
      "definition": "A real number that is not rational.",
      "prerequisite_concept_ids": [
        "r012:concept:real-number-as-cut",
        "r012:concept:rational-number"
      ],
      "source_label": "irrational number",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_complex"
      ]
    },
    {
      "concept_id": "r012:concept:isolated-vertex",
      "definition": "A vertex of degree zero.",
      "prerequisite_concept_ids": [
        "r012:concept:vertex-degree"
      ],
      "source_label": "isolated vertex",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_eulerham",
        "r012:unit:s_ramsey_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:isomer",
      "definition": "A compound sharing a molecular formula with another compound but having a different structural arrangement.",
      "prerequisite_concept_ids": [],
      "source_label": "isomer",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_polya",
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:isomer-enumeration",
      "definition": "Counting chemical substitution patterns modulo molecular symmetries.",
      "prerequisite_concept_ids": [
        "r012:concept:polya-enumeration-theorem",
        "r012:concept:dihedral-group"
      ],
      "source_label": "isomer enumeration",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:k-colorable",
      "definition": "A graph that admits a proper coloring using at most k colors.",
      "prerequisite_concept_ids": [
        "r012:concept:proper-coloring"
      ],
      "source_label": "k-colorable",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_color"
      ]
    },
    {
      "concept_id": "r012:concept:kruskal-algorithm",
      "definition": "Process edges in nondecreasing weight order and admit exactly those that do not create a cycle.",
      "prerequisite_concept_ids": [
        "r012:concept:safe-minimum-cut-edge"
      ],
      "source_label": "Kruskal's algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:alg_kruskal"
      ]
    },
    {
      "concept_id": "r012:concept:kuratowski-theorem",
      "definition": "A graph is planar exactly when it contains no subgraph homeomorphic to K_5 or K_{3,3}.",
      "prerequisite_concept_ids": [
        "r012:concept:planar-graph",
        "r012:concept:graph-homeomorphism",
        "r012:concept:complete-bipartite-graph"
      ],
      "source_label": "Kuratowski's Theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_kuratowski",
        "r012:unit:fig_petersen-graph-k33"
      ]
    },
    {
      "concept_id": "r012:concept:l-tile-rectangle-recurrence",
      "definition": "A recurrence obtained by decomposing tilings of a 2 by n rectangle using unit squares and rotatable L-shaped triominoes.",
      "prerequisite_concept_ids": [
        "r012:concept:recurrence-relation"
      ],
      "source_label": "recurrence for tiling a 2 by n rectangle with squares and L-tiles",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:a4561d5ffe8f5b7ea7d9b05c"
      ]
    },
    {
      "concept_id": "r012:concept:labeled-graph",
      "definition": "A graph whose vertices are distinguished by assigned labels.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "labeled graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:labeled-tree",
      "definition": "A tree whose vertices are distinguished by labels from a specified set.",
      "prerequisite_concept_ids": [
        "r012:concept:tree"
      ],
      "source_label": "labeled tree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_counting-trees",
        "r012:unit:fig_trees-5verts"
      ]
    },
    {
      "concept_id": "r012:concept:labeled-unlabeled-antichain-certificate",
      "definition": "Select from each flow-derived chain the first element whose prime copy is labeled and double-prime copy is unlabeled; the selected elements form a maximum antichain.",
      "prerequisite_concept_ids": [
        "r012:concept:flow-derived-chain-partition",
        "r012:concept:dilworth-theorem"
      ],
      "source_label": "labeled/unlabeled antichain certificate",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_chain-partition"
      ]
    },
    {
      "concept_id": "r012:concept:large-integer-arithmetic",
      "definition": "Exact arithmetic on integers whose size makes efficient computational representation and algorithms practically important.",
      "prerequisite_concept_ids": [
        "r012:concept:number-theory"
      ],
      "source_label": "large integer arithmetic",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_inclusion-exclusion_discussion"
      ]
    },
    {
      "concept_id": "r012:concept:lattice",
      "definition": "A poset in which each pair of elements has both a greatest lower bound and a least upper bound.",
      "prerequisite_concept_ids": [
        "r012:concept:poset"
      ],
      "source_label": "lattice",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_subset-lattice"
      ]
    },
    {
      "concept_id": "r012:concept:lattice-path",
      "definition": "A path through integer lattice points using a prescribed set of step directions.",
      "prerequisite_concept_ids": [
        "r012:concept:counting"
      ],
      "source_label": "lattice path",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_strings_bin-coeff",
        "r012:unit:fig_latticepath",
        "r012:unit:exa_lattice-Catalan",
        "r012:unit:s_strings_lattice-paths-binomial-thm_activity"
      ]
    },
    {
      "concept_id": "r012:concept:leaf",
      "definition": "A vertex of degree one in a tree.",
      "prerequisite_concept_ids": [
        "r012:concept:tree",
        "r012:concept:vertex-degree"
      ],
      "source_label": "leaf",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:prop_tree-leaves"
      ]
    },
    {
      "concept_id": "r012:concept:least-common-multiple",
      "definition": "The smallest positive integer divisible by each integer in a given finite collection.",
      "prerequisite_concept_ids": [
        "r012:concept:prime-factorization"
      ],
      "source_label": "least common multiple",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_number",
        "r012:unit:s_genfunction_exercises",
        "r012:unit:auto:e3dfb8524ffbb34b5062db90",
        "r012:unit:auto:ad5800950b29d7f51c43a73e",
        "r012:unit:auto:6b0d982902d4e6cfc0dfed45",
        "r012:unit:auto:921b776e937d50a2fd4c2c37",
        "r012:unit:auto:9da8ebe78f63c221b5b6bc64",
        "r012:unit:auto:3a3cdb7defb6ad5b83822a4f",
        "r012:unit:auto:5a5a5f490053509f506e2e65",
        "r012:unit:ex_genfunction_ineq-messy"
      ]
    },
    {
      "concept_id": "r012:concept:least-omitted-positive-integer",
      "definition": "Every proper subset of the positive integers omits a unique least positive integer.",
      "prerequisite_concept_ids": [
        "r012:concept:positive-integer-induction",
        "r012:concept:total-order"
      ],
      "source_label": "least omitted positive integer",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_decimal"
      ]
    },
    {
      "concept_id": "r012:concept:left-child",
      "definition": "The first of the two ordered children at an internal RUBOT vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:ordered-tree",
        "r012:concept:tree-child"
      ],
      "source_label": "left child",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots"
      ]
    },
    {
      "concept_id": "r012:concept:line-arrangement",
      "definition": "A finite family of lines considered through its intersection pattern and induced regions.",
      "prerequisite_concept_ids": [
        "r012:concept:geometry"
      ],
      "source_label": "arrangement of lines",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_geom",
        "r012:unit:fig_linesregions",
        "r012:unit:s_recurrence_intro_lines",
        "r012:unit:fig_geomregions",
        "r012:unit:ex_recurrence_lines-solved"
      ]
    },
    {
      "concept_id": "r012:concept:line-region-recurrence",
      "definition": "For lines in general position, the recurrence r_(n+1)=r_n+n+1 obtained because a new line is cut into n+1 unbounded or bounded pieces and creates one new region per piece.",
      "prerequisite_concept_ids": [
        "r012:concept:line-arrangement",
        "r012:concept:recurrence"
      ],
      "source_label": "recurrence for regions determined by lines",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_intro_lines",
        "r012:unit:fig_geomregions",
        "r012:unit:ex_recurrence_lines-solved"
      ]
    },
    {
      "concept_id": "r012:concept:linear-diophantine-equation",
      "definition": "An equation am+bn=c whose coefficients and sought values are integers.",
      "prerequisite_concept_ids": [
        "r012:concept:greatest-common-divisor"
      ],
      "source_label": "linear Diophantine equation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_gcd-dioph"
      ]
    },
    {
      "concept_id": "r012:concept:linear-extension",
      "definition": "A total order on the ground set that preserves every comparison of the original partial order.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order",
        "r012:concept:linear-order"
      ],
      "source_label": "linear extension",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_sorting",
        "r012:unit:fig_posets_lin-extn"
      ]
    },
    {
      "concept_id": "r012:concept:linear-operator",
      "definition": "A map from a vector space to itself that preserves vector addition and scalar multiplication.",
      "prerequisite_concept_ids": [
        "r012:concept:real-vector-space",
        "r012:concept:function"
      ],
      "source_label": "linear operator",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:ba2f054b693f6319b15736f2",
        "r012:unit:s_recurrence_rigorous_principal"
      ]
    },
    {
      "concept_id": "r012:concept:linear-order",
      "definition": "Another name for a total order, emphasizing that all elements lie on one comparison line.",
      "prerequisite_concept_ids": [
        "r012:concept:total-order"
      ],
      "source_label": "linear order",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:s_networkflow_labeling-algorithm",
        "r012:unit:alg_labeling"
      ]
    },
    {
      "concept_id": "r012:concept:linear-programming",
      "definition": "Optimization of a linear objective subject to linear constraints and specified variable domains.",
      "prerequisite_concept_ids": [],
      "source_label": "linear programming",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_integer-programming"
      ]
    },
    {
      "concept_id": "r012:concept:linear-recurrence-classification",
      "definition": "Recognition of whether recurrence expressions are linear in their sequence terms, allowing coefficients to depend on the index.",
      "prerequisite_concept_ids": [
        "r012:concept:linear-recurrence-equation"
      ],
      "source_label": "classification of linear and nonlinear recurrences",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:recurrence_PI_linear"
      ]
    },
    {
      "concept_id": "r012:concept:linear-recurrence-equation",
      "definition": "A recurrence equation in which the relevant terms occur linearly.",
      "prerequisite_concept_ids": [
        "r012:concept:recurrence-equation",
        "r012:concept:recurrence-relation",
        "r012:concept:sequence"
      ],
      "source_label": "linear recurrence equation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_recurrence",
        "r012:unit:auto:b2a4979434434bc7233ca327",
        "r012:unit:s_recurrence_linear",
        "r012:unit:rqs-recurrence_linear",
        "r012:unit:rq-recurrence_linear-matching",
        "r012:unit:s_recurrence_solving",
        "r012:unit:s_recurrence_solving_homogeneous",
        "r012:unit:s_recurrence_solving_nonhomogeneous",
        "r012:unit:rq-recurrence_solving-solve-plus-4",
        "r012:unit:rq-recurrence_solving-solve-plus-deg-two",
        "r012:unit:rq-recurrence_solving-async-nonlinear",
        "r012:unit:s_recurrence_rigorous",
        "r012:unit:thm_advance",
        "r012:unit:lem_base",
        "r012:unit:lem_particular",
        "r012:unit:auto:c52c9183ba4135b30d2552a6",
        "r012:unit:lem_rr"
      ]
    },
    {
      "concept_id": "r012:concept:linearity-of-expectation",
      "definition": "Expectation of a finite sum equals the sum of the expectations.",
      "prerequisite_concept_ids": [
        "r012:concept:expected-value"
      ],
      "source_label": "linearity of expectation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:prop_linearexpect",
        "r012:unit:s_ramsey_probability"
      ]
    },
    {
      "concept_id": "r012:concept:linked-list",
      "definition": "A sequence-like data structure whose nodes point to their successor, with variants that may include additional links.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence"
      ],
      "source_label": "linked list",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro"
      ]
    },
    {
      "concept_id": "r012:concept:little-o",
      "definition": "An asymptotic relation in which one function becomes negligible relative to another.",
      "prerequisite_concept_ids": [
        "r012:concept:big-o"
      ],
      "source_label": "little o notation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_big-oh"
      ]
    },
    {
      "concept_id": "r012:concept:local-lemma-conditional-induction",
      "definition": "Bound each bad event conditioned on fewer avoided events by partitioning dependencies and nondependencies.",
      "prerequisite_concept_ids": [
        "r012:concept:asymmetric-lovasz-local-lemma"
      ],
      "source_label": "conditional induction in the Local Lemma",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:lem_LLL"
      ]
    },
    {
      "concept_id": "r012:concept:local-lemma-parameter-balancing",
      "definition": "Choose x,y,p,t so every exponential penalty remains controlled and t has order n^2/log^2 n.",
      "prerequisite_concept_ids": [
        "r012:concept:local-lemma-ramsey-lower-bound"
      ],
      "source_label": "Local-Lemma parameter balancing",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_applying-local-lemma"
      ]
    },
    {
      "concept_id": "r012:concept:local-lemma-ramsey-lower-bound",
      "definition": "Apply dependency-sensitive avoidance to triangle and independent-set events to obtain an n^2/log^2 n lower bound for R(3,n).",
      "prerequisite_concept_ids": [
        "r012:concept:asymmetric-lovasz-local-lemma",
        "r012:concept:ramsey-number"
      ],
      "source_label": "Local-Lemma Ramsey lower bound",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_applying-local-lemma"
      ]
    },
    {
      "concept_id": "r012:concept:logical-conjunction",
      "definition": "A compound proposition true exactly when both component propositions are true.",
      "prerequisite_concept_ids": [
        "r012:concept:proposition"
      ],
      "source_label": "logical conjunction",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_notation"
      ]
    },
    {
      "concept_id": "r012:concept:logical-disjunction",
      "definition": "A compound proposition true when at least one component proposition is true.",
      "prerequisite_concept_ids": [
        "r012:concept:proposition"
      ],
      "source_label": "logical disjunction",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_notation"
      ]
    },
    {
      "concept_id": "r012:concept:logical-equivalence",
      "definition": "The biconditional relation expressed by 'if and only if'.",
      "prerequisite_concept_ids": [
        "r012:concept:logical-implication"
      ],
      "source_label": "logical equivalence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_notation"
      ]
    },
    {
      "concept_id": "r012:concept:logical-implication",
      "definition": "A conditional relation between propositions denoted by a double arrow.",
      "prerequisite_concept_ids": [
        "r012:concept:proposition"
      ],
      "source_label": "logical implication",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_notation"
      ]
    },
    {
      "concept_id": "r012:concept:logical-negation",
      "definition": "The operation that reverses the truth value of a proposition.",
      "prerequisite_concept_ids": [
        "r012:concept:proposition"
      ],
      "source_label": "logical negation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_equivalence"
      ]
    },
    {
      "concept_id": "r012:concept:logical-quantifier",
      "definition": "A symbol expressing universal or existential scope over a domain.",
      "prerequisite_concept_ids": [
        "r012:concept:predicate"
      ],
      "source_label": "logical quantifier",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_notation"
      ]
    },
    {
      "concept_id": "r012:concept:loose-point",
      "definition": "A one-element component of a poset, equivalently an isolated point in its comparability graph.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-component"
      ],
      "source_label": "loose point",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:lower-bound",
      "definition": "A value known not to exceed the quantity being bounded.",
      "prerequisite_concept_ids": [],
      "source_label": "lower bound",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_applying-local-lemma"
      ]
    },
    {
      "concept_id": "r012:concept:markov-chain",
      "definition": "A finite-state process whose next-state distribution depends only on the current state through fixed probabilities.",
      "prerequisite_concept_ids": [
        "r012:concept:conditional-probability"
      ],
      "source_label": "Markov chain",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_markov-chains"
      ]
    },
    {
      "concept_id": "r012:concept:markov-inequality",
      "definition": "For a random variable X and k>0, P(|X|>=k) is at most E(|X|)/k.",
      "prerequisite_concept_ids": [
        "r012:concept:random-variable",
        "r012:concept:expected-value"
      ],
      "source_label": "Markov's inequality",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_markov"
      ]
    },
    {
      "concept_id": "r012:concept:matching",
      "definition": "A set of graph edges no two of which share an endpoint.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "matching",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_bip-match"
      ]
    },
    {
      "concept_id": "r012:concept:matching-assignment-model",
      "definition": "Represent compatible one-to-one assignments as edges of a bipartite graph and optimize the resulting matching.",
      "prerequisite_concept_ids": [
        "r012:concept:maximum-bipartite-matching"
      ],
      "source_label": "matching assignment model",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:matching-obstruction-certificate",
      "definition": "A set in the first bipartition class with too few neighbors proves that not all its vertices can be saturated.",
      "prerequisite_concept_ids": [
        "r012:concept:hall-theorem"
      ],
      "source_label": "matching obstruction certificate",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:matching-saturation",
      "definition": "A matching saturates a vertex when one of its edges is incident with that vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:matching"
      ],
      "source_label": "vertex saturation by a matching",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_bip-match"
      ]
    },
    {
      "concept_id": "r012:concept:mathematical-induction",
      "definition": "A proof principle establishing a statement at a base case and propagating it through an inductive step.",
      "prerequisite_concept_ids": [
        "r012:concept:positive-integer"
      ],
      "source_label": "mathematical induction",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_induction",
        "r012:unit:auto:157db7e274f439b81e0dec9b",
        "r012:unit:s_background_formal-num-sys",
        "r012:unit:s_background_add",
        "r012:unit:s_background_mult",
        "r012:unit:s_background_exp"
      ]
    },
    {
      "concept_id": "r012:concept:mathematical-symbol-font",
      "definition": "The typeface selection used for mathematical glyphs.",
      "prerequisite_concept_ids": [],
      "source_label": "font for mathematical symbols",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:backmatter"
      ]
    },
    {
      "concept_id": "r012:concept:max-flow-min-cut-theorem",
      "definition": "The maximum value of a feasible source-to-sink flow equals the minimum capacity of a source-sink cut.",
      "prerequisite_concept_ids": [
        "r012:concept:network-flow",
        "r012:concept:ford-fulkerson-labeling-algorithm"
      ],
      "source_label": "max-flow min-cut theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_labeling-algorithm",
        "r012:unit:s_networkflow_example"
      ]
    },
    {
      "concept_id": "r012:concept:maximal-chain",
      "definition": "A chain not properly contained in another chain.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-chain"
      ],
      "source_label": "maximal chain",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_dilworth"
      ]
    },
    {
      "concept_id": "r012:concept:maximal-element",
      "definition": "An element having no strictly larger element in the poset.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order"
      ],
      "source_label": "maximal element",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_dilworth"
      ]
    },
    {
      "concept_id": "r012:concept:maximum-bipartite-matching",
      "definition": "A bipartite matching containing as many edges as possible.",
      "prerequisite_concept_ids": [
        "r012:concept:bipartite-matching"
      ],
      "source_label": "maximum bipartite matching",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_bip-match"
      ]
    },
    {
      "concept_id": "r012:concept:maximum-chain",
      "definition": "A chain of maximum cardinality in a poset.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-chain",
        "r012:concept:poset-height"
      ],
      "source_label": "maximum chain",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_dilworth",
        "r012:unit:fig_height5"
      ]
    },
    {
      "concept_id": "r012:concept:maximum-degree",
      "definition": "The largest vertex degree occurring in a graph.",
      "prerequisite_concept_ids": [
        "r012:concept:vertex-degree"
      ],
      "source_label": "maximum degree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:maximum-flow",
      "definition": "A feasible network flow having greatest possible value.",
      "prerequisite_concept_ids": [
        "r012:concept:network-flow",
        "r012:concept:flow-value"
      ],
      "source_label": "maximum flow",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_flows-cuts"
      ]
    },
    {
      "concept_id": "r012:concept:merge-sort",
      "definition": "A recursive sorting algorithm that sorts sublists and merges the resulting ordered lists.",
      "prerequisite_concept_ids": [
        "r012:concept:sorting",
        "r012:concept:recursion"
      ],
      "source_label": "Merge Sort",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_recursion_sorting",
        "r012:unit:s_posets_sorting"
      ]
    },
    {
      "concept_id": "r012:concept:minimal-element",
      "definition": "An element having no strictly smaller element in the poset.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order"
      ],
      "source_label": "minimal element",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_dilworth",
        "r012:unit:fig_height5"
      ]
    },
    {
      "concept_id": "r012:concept:minimal-interval-representation",
      "definition": "The canonical integer-endpoint representation built from the ordered distinct down sets and up sets of an interval order.",
      "prerequisite_concept_ids": [
        "r012:concept:interval-representation",
        "r012:concept:down-set",
        "r012:concept:up-set",
        "r012:concept:integer-endpoint"
      ],
      "source_label": "minimal interval representation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intervalorder_findrep",
        "r012:unit:thm_intord-minrep",
        "r012:unit:fig_10ptintorder"
      ]
    },
    {
      "concept_id": "r012:concept:minimum-cut",
      "definition": "A source-sink cut having least possible capacity.",
      "prerequisite_concept_ids": [
        "r012:concept:network-cut",
        "r012:concept:cut-capacity"
      ],
      "source_label": "minimum cut",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_flows-cuts"
      ]
    },
    {
      "concept_id": "r012:concept:minimum-spanning-tree",
      "definition": "A spanning tree whose total edge weight is minimum among all spanning trees of a weighted graph.",
      "prerequisite_concept_ids": [
        "r012:concept:spanning-tree",
        "r012:concept:weighted-graph",
        "r012:concept:optimization"
      ],
      "source_label": "minimum-weight spanning tree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_opt",
        "r012:unit:fig_spantree-1",
        "r012:unit:s_graphalgorithms_min-wt-span"
      ]
    },
    {
      "concept_id": "r012:concept:minimum-spanning-tree-algorithm-history",
      "definition": "The publication and rediscovery lineage connecting Jarnik, Kruskal, Prim, and Dijkstra.",
      "prerequisite_concept_ids": [
        "r012:concept:kruskal-algorithm",
        "r012:concept:prim-algorithm"
      ],
      "source_label": "history of minimum spanning-tree algorithms",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_historical-notes"
      ]
    },
    {
      "concept_id": "r012:concept:modular-arithmetic",
      "definition": "Arithmetic in which integers are identified when they have the same remainder modulo a fixed positive integer.",
      "prerequisite_concept_ids": [],
      "source_label": "modular arithmetic",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:monotonicity-law",
      "definition": "A law describing how an operation preserves or reverses an order relation.",
      "prerequisite_concept_ids": [
        "r012:concept:total-order"
      ],
      "source_label": "monotonicity law",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_prop-integers"
      ]
    },
    {
      "concept_id": "r012:concept:multigraph",
      "definition": "A graph-like structure that permits loops and multiple edges.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:multiple-edge",
        "r012:concept:graph-loop"
      ],
      "source_label": "multigraph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_multigraphs"
      ]
    },
    {
      "concept_id": "r012:concept:multinomial-coefficient",
      "definition": "The number of ways to divide a labeled n-element set into ordered groups of prescribed nonnegative sizes summing to n.",
      "prerequisite_concept_ids": [
        "r012:concept:binomial-coefficient",
        "r012:concept:factorial"
      ],
      "source_label": "multinomial coefficient",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_strings_multinom",
        "r012:unit:exa_strings_multinom"
      ]
    },
    {
      "concept_id": "r012:concept:multinomial-theorem",
      "definition": "The expansion of a nonnegative integer power of a sum of finitely many terms using multinomial coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:multinomial-coefficient",
        "r012:concept:binomial-theorem"
      ],
      "source_label": "Multinomial Theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm-strings-multinomial",
        "r012:unit:s_strings_lattice-paths-binomial-thm_activity"
      ]
    },
    {
      "concept_id": "r012:concept:multiple-edge",
      "definition": "One of two or more distinct edges having the same pair of endpoints.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "multiple edge",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_multigraphs"
      ]
    },
    {
      "concept_id": "r012:concept:multiplication-laws",
      "definition": "Left and right distributivity, associativity, identity, zero, and commutativity derived by induction.",
      "prerequisite_concept_ids": [
        "r012:concept:recursive-multiplication",
        "r012:concept:addition-laws"
      ],
      "source_label": "laws of multiplication",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_mult"
      ]
    },
    {
      "concept_id": "r012:concept:multiplication-monotonicity",
      "definition": "Multiplication by a nonnegative factor preserves weak order and by a positive factor preserves strict order.",
      "prerequisite_concept_ids": [
        "r012:concept:natural-number-order",
        "r012:concept:integer-multiplication"
      ],
      "source_label": "monotonicity of multiplication",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_total-order-N"
      ]
    },
    {
      "concept_id": "r012:concept:multiplicative-cancellation",
      "definition": "Equal products with the same nonzero factor have equal remaining factors.",
      "prerequisite_concept_ids": [
        "r012:concept:multiplication-monotonicity"
      ],
      "source_label": "multiplicative cancellation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_total-order-N"
      ]
    },
    {
      "concept_id": "r012:concept:multiplicative-inverse",
      "definition": "For a nonzero fraction (a,b), the reciprocal (b,a), whose product with it is one.",
      "prerequisite_concept_ids": [
        "r012:concept:rational-arithmetic"
      ],
      "source_label": "multiplicative inverse",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:multiset-generating-function",
      "definition": "The coefficient of x^k in (1-x)^(-n) counts size-k multisets from n types, equivalently distributions of k indistinguishable objects to n recipients.",
      "prerequisite_concept_ids": [
        "r012:concept:generating-function-distribution-model",
        "r012:concept:binomial-coefficient"
      ],
      "source_label": "generating function for multisets",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_distributions",
        "r012:unit:exa_genfunction_multisets",
        "r012:unit:auto:d7c45bbaac6cda937a07c30e"
      ]
    },
    {
      "concept_id": "r012:concept:naive-recursion-cost",
      "definition": "Growth in execution time caused by repeatedly recomputing overlapping recursive subproblems.",
      "prerequisite_concept_ids": [
        "r012:concept:recursive-evaluation",
        "r012:concept:computational-complexity"
      ],
      "source_label": "computational cost of naive recursive evaluation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_discussion",
        "r012:unit:recurrence_discussion_takeaways"
      ]
    },
    {
      "concept_id": "r012:concept:natural-number-order",
      "definition": "The relation m≤n defined by the existence of a nonnegative p with m+p=n.",
      "prerequisite_concept_ids": [
        "r012:concept:nonnegative-integer",
        "r012:concept:integer-addition"
      ],
      "source_label": "order on nonnegative integers",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_total-order-N"
      ]
    },
    {
      "concept_id": "r012:concept:natural-order-totality",
      "definition": "Reflexivity, antisymmetry, transitivity, and inductive comparability make the order total.",
      "prerequisite_concept_ids": [
        "r012:concept:natural-number-order",
        "r012:concept:mathematical-induction"
      ],
      "source_label": "totality of natural-number order",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_total-order-N"
      ]
    },
    {
      "concept_id": "r012:concept:necklace",
      "definition": "A circular arrangement of beads considered up to the symmetries specified by the problem.",
      "prerequisite_concept_ids": [
        "r012:concept:enumeration"
      ],
      "source_label": "necklace",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_enum",
        "r012:unit:fig_intro_necklace"
      ]
    },
    {
      "concept_id": "r012:concept:negated-relation",
      "definition": "Notation asserting that an ordered pair does not belong to a relation.",
      "prerequisite_concept_ids": [
        "r012:concept:binary-relation",
        "r012:concept:logical-negation"
      ],
      "source_label": "negated relation membership",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_equivalence"
      ]
    },
    {
      "concept_id": "r012:concept:negative-half-binomial-coefficient",
      "definition": "The closed form binom(-1/2,k)=(-1)^k binom(2k,k)/2^(2k).",
      "prerequisite_concept_ids": [
        "r012:concept:generalized-binomial-coefficient",
        "r012:concept:falling-product-recurrence"
      ],
      "source_label": "negative one-half generalized binomial coefficient",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:l_newbinom",
        "r012:unit:auto:0bd3b62b200da00131d43e75"
      ]
    },
    {
      "concept_id": "r012:concept:network-cut",
      "definition": "A partition V=L union U with the source in L and the sink in U.",
      "prerequisite_concept_ids": [
        "r012:concept:flow-network"
      ],
      "source_label": "cut",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_flows-cuts",
        "r012:unit:s_networkflow_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:network-flow",
      "definition": "Assignment of quantities to directed network edges subject to capacity and conservation constraints.",
      "prerequisite_concept_ids": [
        "r012:concept:digraph",
        "r012:concept:optimization"
      ],
      "source_label": "network flow",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:ch_networkflow",
        "r012:unit:s_networkflow_intro",
        "r012:unit:s_networkflow_flows-cuts",
        "r012:unit:s_networkflow_augmenting",
        "r012:unit:s_networkflow_labeling-algorithm",
        "r012:unit:s_networkflow_example",
        "r012:unit:s_networkflow_integer-programming",
        "r012:unit:s_networkflow_exercises",
        "r012:unit:ch_flowapplications",
        "r012:unit:s_flowapplications_intro"
      ]
    },
    {
      "concept_id": "r012:concept:network-flow-linear-program",
      "definition": "The formulation of maximum network flow as a linear optimization problem over edge-flow variables.",
      "prerequisite_concept_ids": [
        "r012:concept:network-flow",
        "r012:concept:linear-programming"
      ],
      "source_label": "network flow as linear programming",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_integer-programming"
      ]
    },
    {
      "concept_id": "r012:concept:network-flow-optimality-certificate",
      "definition": "A cut whose capacity equals a feasible flow value, certifying that both are optimal.",
      "prerequisite_concept_ids": [
        "r012:concept:flow-cut-capacity-bound"
      ],
      "source_label": "network-flow optimality certificate",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_flows-cuts",
        "r012:unit:s_networkflow_labeling-algorithm",
        "r012:unit:s_networkflow_example"
      ]
    },
    {
      "concept_id": "r012:concept:network-source-and-sink",
      "definition": "The distinguished initial and terminal vertices of a flow network; source edges point outward and sink edges point inward.",
      "prerequisite_concept_ids": [
        "r012:concept:flow-network"
      ],
      "source_label": "source and sink",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_intro"
      ]
    },
    {
      "concept_id": "r012:concept:noncommutative-operation",
      "definition": "A binary operation for which changing the order of the operands can change the result.",
      "prerequisite_concept_ids": [],
      "source_label": "noncommutative operation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_perm-groups"
      ]
    },
    {
      "concept_id": "r012:concept:nonconstant-coefficient-recurrence",
      "definition": "A linear recurrence equation in which one or more coefficients may depend on the sequence index.",
      "prerequisite_concept_ids": [
        "r012:concept:linear-recurrence-equation"
      ],
      "source_label": "linear recurrence equation with nonconstant coefficients",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_linear",
        "r012:unit:rq-recurrence_linear-matching"
      ]
    },
    {
      "concept_id": "r012:concept:nonhomogeneous-forcing-generating-function",
      "definition": "The generating function for the nonzero right-hand-side sequence, adjusted for the recurrence's starting index and combined with shifted solution-series terms.",
      "prerequisite_concept_ids": [
        "r012:concept:generating-function-recurrence-method",
        "r012:concept:nonhomogeneous-linear-recurrence"
      ],
      "source_label": "generating function of the forcing sequence in a nonhomogeneous recurrence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ex_recurrence_gf-nonhomog"
      ]
    },
    {
      "concept_id": "r012:concept:nonhomogeneous-linear-recurrence",
      "definition": "A linear recurrence equation whose forcing function is not identically zero.",
      "prerequisite_concept_ids": [
        "r012:concept:linear-recurrence-equation"
      ],
      "source_label": "nonhomogeneous linear recurrence equation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_linear",
        "r012:unit:rq-recurrence_linear-matching",
        "r012:unit:s_recurrence_solving_nonhomogeneous",
        "r012:unit:auto:4a09aa7241b0bf6a931d0955",
        "r012:unit:auto:2b9501b6517e77e868e24689",
        "r012:unit:ex_recurrence_lines-solved",
        "r012:unit:auto:025bf0a72a4db690049c74bf",
        "r012:unit:rq-recurrence_solving-async-nonlinear"
      ]
    },
    {
      "concept_id": "r012:concept:nonincreasing-sequence",
      "definition": "A sequence whose successive terms never increase.",
      "prerequisite_concept_ids": [],
      "source_label": "non-increasing sequence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_enum",
        "r012:unit:s_kitchensink_zero-one-matrices"
      ]
    },
    {
      "concept_id": "r012:concept:nonisomorphic-graph",
      "definition": "Graphs for which no adjacency-preserving bijection exists between their vertex sets.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-isomorphism"
      ],
      "source_label": "nonisomorphic graphs",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps",
        "r012:unit:s_polya_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:nonnegative-integer",
      "definition": "An integer greater than or equal to zero.",
      "prerequisite_concept_ids": [],
      "source_label": "non-negative integer",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_ErdosSzekeres",
        "r012:unit:s_strings_comb-proof",
        "r012:unit:thm_binomial",
        "r012:unit:exa_inclusion-exclusion_int-solns",
        "r012:unit:auto:404b9eaf4b1ef3eb26f316ad",
        "r012:unit:auto:8f3500f97b0ab7c55c94505a",
        "r012:unit:s_background_int-union",
        "r012:unit:s_background_formal-num-sys",
        "r012:unit:s_background_add",
        "r012:unit:s_background_mult",
        "r012:unit:s_background_exp"
      ]
    },
    {
      "concept_id": "r012:concept:notation-list",
      "definition": "An automatically generated reference list of mathematical notation used in the book.",
      "prerequisite_concept_ids": [
        "r012:concept:back-matter"
      ],
      "source_label": "list of notation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:890b13ffad581b51ada6044f",
        "r012:unit:backmatter"
      ]
    },
    {
      "concept_id": "r012:concept:np-class",
      "definition": "The class of decision problems whose yes instances have certificates verifiable in polynomial time.",
      "prerequisite_concept_ids": [
        "r012:concept:polynomial-time"
      ],
      "source_label": "NP",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_exact"
      ]
    },
    {
      "concept_id": "r012:concept:number-system-construction-sequence",
      "definition": "The staged construction of natural, integer, rational, real, and complex number systems.",
      "prerequisite_concept_ids": [
        "r012:concept:set-theoretic-foundations"
      ],
      "source_label": "number-system construction sequence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:app_background"
      ]
    },
    {
      "concept_id": "r012:concept:number-theory",
      "definition": "The study of integers and their arithmetic properties.",
      "prerequisite_concept_ids": [
        "r012:concept:positive-integer"
      ],
      "source_label": "number theory",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_number",
        "r012:unit:s_inclusion-exclusion_euler-phi",
        "r012:unit:s_kitchensink_arithmetic-combinatorics"
      ]
    },
    {
      "concept_id": "r012:concept:numerator",
      "definition": "The upper component of a fraction.",
      "prerequisite_concept_ids": [
        "r012:concept:fraction"
      ],
      "source_label": "numerator",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:octave",
      "definition": "A musical interval spanning eight scale degrees and conventionally corresponding to a doubling of frequency.",
      "prerequisite_concept_ids": [],
      "source_label": "octave",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:odd-part-partition",
      "definition": "An integer partition in which every positive part is odd.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-partition"
      ],
      "source_label": "partition into odd parts",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:fig_genfunction_partsof8",
        "r012:unit:thm_partition",
        "r012:unit:auto:c1cbbffbb5bf258ea18be45d",
        "r012:unit:s_genfunction_discussion",
        "r012:unit:auto:c53a9727c6ac71ed663831ee",
        "r012:unit:auto:e0f50e92137238f006185b9f"
      ]
    },
    {
      "concept_id": "r012:concept:offline-algorithm",
      "definition": "An algorithm that may inspect the complete input before making its decisions.",
      "prerequisite_concept_ids": [],
      "source_label": "offline algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_online"
      ]
    },
    {
      "concept_id": "r012:concept:online-algorithm",
      "definition": "An algorithm that must make irrevocable decisions as input is revealed sequentially.",
      "prerequisite_concept_ids": [],
      "source_label": "online algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_online"
      ]
    },
    {
      "concept_id": "r012:concept:online-graph-coloring-game",
      "definition": "Builder reveals vertices and prior adjacencies while Assigner must immediately choose a proper color.",
      "prerequisite_concept_ids": [
        "r012:concept:online-algorithm",
        "r012:concept:proper-coloring"
      ],
      "source_label": "online graph-coloring game",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_online"
      ]
    },
    {
      "concept_id": "r012:concept:online-poset-antichain-partition",
      "definition": "Assign each arriving poset point to an antichain indexed by its longest upward and downward chain lengths.",
      "prerequisite_concept_ids": [
        "r012:concept:online-algorithm",
        "r012:concept:poset-antichain",
        "r012:concept:poset-height"
      ],
      "source_label": "online poset antichain partition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_online"
      ]
    },
    {
      "concept_id": "r012:concept:open-statement",
      "definition": "A statement involving a variable whose truth depends on the value assigned to that variable.",
      "prerequisite_concept_ids": [
        "r012:concept:positive-integer",
        "r012:concept:predicate"
      ],
      "source_label": "open statement",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_induction",
        "r012:unit:s_background_notation"
      ]
    },
    {
      "concept_id": "r012:concept:operating-system",
      "definition": "System software managing computing hardware and application execution.",
      "prerequisite_concept_ids": [],
      "source_label": "operating system",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:optimization",
      "definition": "Selection of a feasible object that maximizes or minimizes an objective.",
      "prerequisite_concept_ids": [
        "r012:concept:algorithm"
      ],
      "source_label": "optimization",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:ch_networkflow",
        "r012:unit:s_networkflow_intro",
        "r012:unit:s_networkflow_flows-cuts",
        "r012:unit:s_networkflow_integer-programming"
      ]
    },
    {
      "concept_id": "r012:concept:ordered-coin-sequence-generating-function",
      "definition": "An ordinary generating function whose coefficients count denomination sequences in which the order of inserted coins matters.",
      "prerequisite_concept_ids": [
        "r012:concept:coin-change-generating-function",
        "r012:concept:string"
      ],
      "source_label": "generating function for ordered coin sequences",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:3a3cdb7defb6ad5b83822a4f",
        "r012:unit:exer_genfunction_coin-toll",
        "r012:unit:auto:46be14a19d3b560435dab10c"
      ]
    },
    {
      "concept_id": "r012:concept:ordered-pair",
      "definition": "A two-coordinate object whose coordinate order is significant.",
      "prerequisite_concept_ids": [],
      "source_label": "ordered pair",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_products"
      ]
    },
    {
      "concept_id": "r012:concept:ordered-tree",
      "definition": "A rooted tree whose children at every vertex have a specified order.",
      "prerequisite_concept_ids": [
        "r012:concept:rooted-tree"
      ],
      "source_label": "ordered tree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots"
      ]
    },
    {
      "concept_id": "r012:concept:ordinary-generating-function",
      "definition": "A generating function of the form sum from n=0 to infinity of a_n x^n, so the coefficient of x^n is a_n.",
      "prerequisite_concept_ids": [
        "r012:concept:generating-function",
        "r012:concept:formal-power-series"
      ],
      "source_label": "ordinary generating function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_exponential",
        "r012:unit:s_genfunction_exercises",
        "r012:unit:auto:e3dfb8524ffbb34b5062db90",
        "r012:unit:auto:a65033c7e640b8b32155ee76",
        "r012:unit:s_genfunction_PI",
        "r012:unit:genfunction_PI_exponential-vs-ordinary"
      ]
    },
    {
      "concept_id": "r012:concept:oriented-graph",
      "definition": "A digraph obtained by assigning one direction to every edge of an underlying graph.",
      "prerequisite_concept_ids": [
        "r012:concept:digraph",
        "r012:concept:graph"
      ],
      "source_label": "oriented graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_shortest-paths",
        "r012:unit:s_networkflow_intro"
      ]
    },
    {
      "concept_id": "r012:concept:outcome",
      "definition": "An elementary member of the outcome set.",
      "prerequisite_concept_ids": [
        "r012:concept:probability-space"
      ],
      "source_label": "outcome",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_intro"
      ]
    },
    {
      "concept_id": "r012:concept:p-class",
      "definition": "The class of decision problems solvable in polynomial time.",
      "prerequisite_concept_ids": [
        "r012:concept:polynomial-time"
      ],
      "source_label": "P",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_exact"
      ]
    },
    {
      "concept_id": "r012:concept:pair-group",
      "definition": "The permutation action induced on two-element subsets by permutations of the underlying vertices.",
      "prerequisite_concept_ids": [
        "r012:concept:symmetric-group",
        "r012:concept:group-action"
      ],
      "source_label": "pair group",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:pairing-axiom",
      "definition": "For any two sets there exists a set whose elements are exactly those two sets.",
      "prerequisite_concept_ids": [
        "r012:concept:zfc-set-theory"
      ],
      "source_label": "axiom of pairing",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_ZFC"
      ]
    },
    {
      "concept_id": "r012:concept:pairwise-disjoint",
      "definition": "A family of sets in which every two distinct members have empty intersection.",
      "prerequisite_concept_ids": [],
      "source_label": "pairwise disjoint",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_enum"
      ]
    },
    {
      "concept_id": "r012:concept:pairwise-independent-random-variables",
      "definition": "Every two distinct real-valued random variables in the family have independent threshold events for all real thresholds.",
      "prerequisite_concept_ids": [
        "r012:concept:random-variable",
        "r012:concept:independent-events"
      ],
      "source_label": "pairwise independent random variables",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:4bd593cb3ed0759f3af2567d"
      ]
    },
    {
      "concept_id": "r012:concept:partial-fraction-coefficient-extraction",
      "definition": "Decomposition of a rational generating function into simpler rational terms with recognizable power-series coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:generating-function",
        "r012:concept:formal-power-series"
      ],
      "source_label": "coefficient extraction by partial fractions",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_distributions",
        "r012:unit:exa_genfunction_partial-fracs",
        "r012:unit:auto:692d3d5206064b390fb35ace"
      ]
    },
    {
      "concept_id": "r012:concept:partial-order",
      "definition": "A reflexive, antisymmetric, and transitive binary relation on a set.",
      "prerequisite_concept_ids": [
        "r012:concept:binary-relation",
        "r012:concept:reflexive-relation",
        "r012:concept:antisymmetric-relation",
        "r012:concept:transitive-relation"
      ],
      "source_label": "partial order",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:s_kitchensink_zero-one-matrices",
        "r012:unit:s_background_order"
      ]
    },
    {
      "concept_id": "r012:concept:particular-plus-homogeneous-solution",
      "definition": "If f_0 is one solution of p(A)f=g, every other solution differs from f_0 by a member of the homogeneous solution space.",
      "prerequisite_concept_ids": [
        "r012:concept:homogeneous-recurrence-solution-space",
        "r012:concept:advancement-operator-equation"
      ],
      "source_label": "particular solution plus homogeneous solution",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:lem_particular",
        "r012:unit:auto:3cdf045c69a328229cf28c05",
        "r012:unit:s_recurrence_solving_nonhomogeneous",
        "r012:unit:auto:4a09aa7241b0bf6a931d0955",
        "r012:unit:auto:2b9501b6517e77e868e24689",
        "r012:unit:ex_recurrence_lines-solved",
        "r012:unit:auto:025bf0a72a4db690049c74bf"
      ]
    },
    {
      "concept_id": "r012:concept:particular-solution",
      "definition": "One solution matching the forcing term of a nonhomogeneous recurrence, combined with the homogeneous solution to obtain the general solution.",
      "prerequisite_concept_ids": [
        "r012:concept:nonhomogeneous-linear-recurrence"
      ],
      "source_label": "particular solution of a nonhomogeneous recurrence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_genfunction"
      ]
    },
    {
      "concept_id": "r012:concept:particular-solution-trial-method",
      "definition": "For p(A)f=g, choose a trial form modeled on the right-hand side with undetermined constants, apply p(A), and determine the constants by matching the resulting coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:nonhomogeneous-linear-recurrence",
        "r012:concept:advancement-operator-polynomial"
      ],
      "source_label": "trial method for a particular solution",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_solving_nonhomogeneous",
        "r012:unit:auto:4a09aa7241b0bf6a931d0955",
        "r012:unit:auto:2b9501b6517e77e868e24689",
        "r012:unit:ex_recurrence_lines-solved",
        "r012:unit:auto:025bf0a72a4db690049c74bf",
        "r012:unit:rq-recurrence_solving-async-nonlinear"
      ]
    },
    {
      "concept_id": "r012:concept:particular-trial-overlap-adjustment",
      "definition": "When a proposed forcing-shaped trial contains terms annihilated by the homogeneous operator, modify the trial, commonly by multiplying by a sufficient power of n or raising polynomial degree, before matching coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:particular-solution-trial-method",
        "r012:concept:homogeneous-linear-recurrence"
      ],
      "source_label": "adjusting a particular trial that overlaps the homogeneous solution",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:2b9501b6517e77e868e24689",
        "r012:unit:ex_recurrence_lines-solved",
        "r012:unit:auto:025bf0a72a4db690049c74bf",
        "r012:unit:rq-recurrence_solving-async-nonlinear"
      ]
    },
    {
      "concept_id": "r012:concept:partition",
      "definition": "A decomposition into mutually disjoint parts that exhaust the original object.",
      "prerequisite_concept_ids": [
        "r012:concept:pairwise-disjoint"
      ],
      "source_label": "partition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:s_intro_enum"
      ]
    },
    {
      "concept_id": "r012:concept:partition-cover-relation",
      "definition": "A cover transfers one unit from an earlier part to a later part under the stated plateau constraints.",
      "prerequisite_concept_ids": [
        "r012:concept:partition-dominance-order"
      ],
      "source_label": "cover relation in partition dominance order",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:prop_partitioncover",
        "r012:unit:s_kitchensink_zero-one-matrices"
      ]
    },
    {
      "concept_id": "r012:concept:partition-dominance-order",
      "definition": "V dominates W when every relevant prefix sum of V is at least the corresponding prefix sum of W.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-partition"
      ],
      "source_label": "dominance order on integer partitions",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_zero-one-matrices"
      ]
    },
    {
      "concept_id": "r012:concept:partition-generating-function",
      "definition": "The infinite product over positive part sizes whose coefficient of x^n is the partition number p_n.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-partition",
        "r012:concept:generating-function",
        "r012:concept:power-series-product"
      ],
      "source_label": "generating function for integer partitions",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_partitions-integer",
        "r012:unit:thm_partition",
        "r012:unit:auto:c1cbbffbb5bf258ea18be45d",
        "r012:unit:auto:e0f50e92137238f006185b9f",
        "r012:unit:auto:5a5a5f490053509f506e2e65",
        "r012:unit:auto:fce61924f5d5515db0dda1a7"
      ]
    },
    {
      "concept_id": "r012:concept:partition-number",
      "definition": "The number p_n of integer partitions of n, with p_0=1 by convention.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-partition",
        "r012:concept:sequence"
      ],
      "source_label": "partition number",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_partitions-integer"
      ]
    },
    {
      "concept_id": "r012:concept:partitioned-event-probability",
      "definition": "An event split into disjoint cases has probability equal to the sum of the case probabilities.",
      "prerequisite_concept_ids": [
        "r012:concept:conditional-probability",
        "r012:concept:disjoint-events"
      ],
      "source_label": "probability over a partition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:exa_twojars"
      ]
    },
    {
      "concept_id": "r012:concept:pascal-triangle",
      "definition": "A triangular arrangement of binomial coefficients in which each interior entry is the sum of the two entries above it.",
      "prerequisite_concept_ids": [
        "r012:concept:binomial-coefficient",
        "r012:concept:recursion"
      ],
      "source_label": "Pascal's triangle",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_bincoeffs",
        "r012:unit:fig_pascal"
      ]
    },
    {
      "concept_id": "r012:concept:path",
      "definition": "A sequence of vertices in which consecutive vertices are adjacent.",
      "prerequisite_concept_ids": [
        "r012:concept:adjacency"
      ],
      "source_label": "path",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_graph",
        "r012:unit:auto:21546ae1bdf04f7552481516",
        "r012:unit:s_networkflow_augmenting",
        "r012:unit:s_networkflow_labeling-algorithm",
        "r012:unit:s_networkflow_example",
        "r012:unit:s_networkflow_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:pattern-inventory",
      "definition": "A generating function whose coefficients count inequivalent patterns with specified color multiplicities.",
      "prerequisite_concept_ids": [
        "r012:concept:polya-enumeration-theorem"
      ],
      "source_label": "pattern inventory",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_polya"
      ]
    },
    {
      "concept_id": "r012:concept:payoff-ratio",
      "definition": "The ratio between a wager's payout and the amount staked.",
      "prerequisite_concept_ids": [
        "r012:concept:fair-game"
      ],
      "source_label": "payoff ratio",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:07a5e2769ec7b1889ef21fcf"
      ]
    },
    {
      "concept_id": "r012:concept:peano-postulates",
      "definition": "Axioms specifying zero, an injective successor, the absence of a predecessor of zero, and induction.",
      "prerequisite_concept_ids": [
        "r012:concept:mathematical-induction"
      ],
      "source_label": "Peano postulates",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_formal-num-sys"
      ]
    },
    {
      "concept_id": "r012:concept:perfect-graph",
      "definition": "A graph for which every induced subgraph has chromatic number equal to clique number.",
      "prerequisite_concept_ids": [
        "r012:concept:induced-subgraph",
        "r012:concept:chromatic-number",
        "r012:concept:clique-number"
      ],
      "source_label": "perfect graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_intgraphcol",
        "r012:unit:s_posets_dilworth-intord"
      ]
    },
    {
      "concept_id": "r012:concept:permutation",
      "definition": "An ordering or rearrangement of distinct positions or objects.",
      "prerequisite_concept_ids": [
        "r012:concept:enumeration"
      ],
      "source_label": "permutation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:s_strings_permutations",
        "r012:unit:exa_strings_perm",
        "r012:unit:prop_strings_permutations",
        "r012:unit:exa_inclusion-exclusion_prop-derange",
        "r012:unit:inclusion-exclusion_PI_perms-count",
        "r012:unit:inclusion-exclusion_PI_perm-prop"
      ]
    },
    {
      "concept_id": "r012:concept:permutation-group",
      "definition": "A set of permutations containing the identity and closed under composition and inverses.",
      "prerequisite_concept_ids": [
        "r012:concept:permutation",
        "r012:concept:function-composition"
      ],
      "source_label": "permutation group",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_perm-groups"
      ]
    },
    {
      "concept_id": "r012:concept:permutation-multiplication",
      "definition": "Composition of permutations, evaluated from right to left.",
      "prerequisite_concept_ids": [
        "r012:concept:cycle-notation",
        "r012:concept:function-composition"
      ],
      "source_label": "permutation multiplication",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_perm-groups"
      ]
    },
    {
      "concept_id": "r012:concept:pigeonhole-principle",
      "definition": "A function from a larger finite set to a smaller finite set maps at least two distinct inputs to the same output.",
      "prerequisite_concept_ids": [
        "r012:concept:function",
        "r012:concept:injection"
      ],
      "source_label": "Pigeon Hole Principle",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_pigeonhole",
        "r012:unit:prop_pigeon"
      ]
    },
    {
      "concept_id": "r012:concept:planar-drawing",
      "definition": "A crossing-free drawing of a planar graph in the plane.",
      "prerequisite_concept_ids": [
        "r012:concept:planar-graph"
      ],
      "source_label": "planar drawing",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:fig_planar",
        "r012:unit:fig_k4-planar"
      ]
    },
    {
      "concept_id": "r012:concept:planar-graph",
      "definition": "A graph admitting a drawing in the plane with no edge crossings except at shared endpoints.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:edge-crossing"
      ],
      "source_label": "planar graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_planar",
        "r012:unit:fig_planar",
        "r012:unit:fig_k4-planar"
      ]
    },
    {
      "concept_id": "r012:concept:planarity",
      "definition": "The property of a graph admitting a planar drawing.",
      "prerequisite_concept_ids": [
        "r012:concept:planar-graph",
        "r012:concept:planar-drawing"
      ],
      "source_label": "planarity",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_planar",
        "r012:unit:thm_kuratowski"
      ]
    },
    {
      "concept_id": "r012:concept:polya-counting",
      "definition": "Enumeration of patterns under group actions using cycle structure.",
      "prerequisite_concept_ids": [
        "r012:concept:enumeration",
        "r012:concept:symmetry-equivalence"
      ],
      "source_label": "Pólya counting",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro"
      ]
    },
    {
      "concept_id": "r012:concept:polya-enumeration-theorem",
      "definition": "The theorem that substituting a color inventory into a permutation group's cycle index yields the generating function for inequivalent colorings.",
      "prerequisite_concept_ids": [
        "r012:concept:symmetry-aware-enumeration",
        "r012:concept:permutation-group",
        "r012:concept:cycle-index",
        "r012:concept:inventory-substitution"
      ],
      "source_label": "Pólya enumeration theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_polya",
        "r012:unit:s_polya_polya"
      ]
    },
    {
      "concept_id": "r012:concept:polya-exercise-synthesis",
      "definition": "Integrated practice with cycle notation, group actions, cycle indices, and inventory substitution.",
      "prerequisite_concept_ids": [
        "r012:concept:cycle-notation",
        "r012:concept:burnside-lemma",
        "r012:concept:polya-enumeration-theorem"
      ],
      "source_label": "Pólya-method exercise synthesis",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:polynomial",
      "definition": "A finite sum of coefficients multiplied by nonnegative integer powers of a variable.",
      "prerequisite_concept_ids": [],
      "source_label": "polynomial",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_complex"
      ]
    },
    {
      "concept_id": "r012:concept:polynomial-expansion",
      "definition": "The expression obtained by multiplying out a polynomial product or power and collecting its terms.",
      "prerequisite_concept_ids": [],
      "source_label": "expansion",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_strings_binom-thm",
        "r012:unit:s_strings_multinom",
        "r012:unit:s_strings_lattice-paths-binomial-thm_activity"
      ]
    },
    {
      "concept_id": "r012:concept:polynomial-time",
      "definition": "Running time bounded above by a fixed polynomial in the input size.",
      "prerequisite_concept_ids": [
        "r012:concept:computational-complexity",
        "r012:concept:big-o"
      ],
      "source_label": "polynomial time",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_complexity",
        "r012:unit:s_basics_big-oh",
        "r012:unit:s_basics_exact"
      ]
    },
    {
      "concept_id": "r012:concept:poset",
      "definition": "A set equipped with a partial order.",
      "prerequisite_concept_ids": [
        "r012:concept:discrete-structures"
      ],
      "source_label": "partially ordered set (poset)",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:ch_posets",
        "r012:unit:s_posets_intro",
        "r012:unit:s_posets_additional-concepts",
        "r012:unit:s_posets_dilworth"
      ]
    },
    {
      "concept_id": "r012:concept:poset-antichain",
      "definition": "A subset of a poset whose distinct elements are pairwise incomparable.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-comparability",
        "r012:concept:poset"
      ],
      "source_label": "antichain",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:thm_dualdilworth",
        "r012:unit:s_flowapplications_chain-partition",
        "r012:unit:s_kitchensink_online"
      ]
    },
    {
      "concept_id": "r012:concept:poset-automorphism",
      "definition": "An isomorphism from a poset to itself.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-isomorphism"
      ],
      "source_label": "poset automorphism",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:poset-chain",
      "definition": "A subset of a poset whose elements are pairwise comparable.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-comparability"
      ],
      "source_label": "chain",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:thm_dilworth"
      ]
    },
    {
      "concept_id": "r012:concept:poset-comparability",
      "definition": "Two elements of a poset are comparable when one is less than or equal to the other.",
      "prerequisite_concept_ids": [
        "r012:concept:poset",
        "r012:concept:partial-order"
      ],
      "source_label": "comparable elements",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:poset-component",
      "definition": "A maximal connected subposet.",
      "prerequisite_concept_ids": [
        "r012:concept:connected-poset",
        "r012:concept:subposet"
      ],
      "source_label": "component of a poset",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:poset-dimension",
      "definition": "The least number of linear extensions whose intersection is the given partial order.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order",
        "r012:concept:linear-extension"
      ],
      "source_label": "poset dimension",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:poset-embedding",
      "definition": "An isomorphism from a poset onto a subposet of another poset.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-isomorphism",
        "r012:concept:subposet"
      ],
      "source_label": "poset embedding",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:poset-height",
      "definition": "The maximum cardinality of a chain in a finite poset.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-chain"
      ],
      "source_label": "height of a poset",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:thm_dualdilworth",
        "r012:unit:fig_height5"
      ]
    },
    {
      "concept_id": "r012:concept:poset-incomparability",
      "definition": "Two elements of a poset are incomparable when neither is less than or equal to the other.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-comparability"
      ],
      "source_label": "incomparable elements",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:fig_compincomp"
      ]
    },
    {
      "concept_id": "r012:concept:poset-isomorphism",
      "definition": "A bijection between ground sets preserving and reflecting the partial order.",
      "prerequisite_concept_ids": [
        "r012:concept:poset",
        "r012:concept:bijection"
      ],
      "source_label": "poset isomorphism",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:poset-network-reconstruction",
      "definition": "Recover comparabilities and extremal elements from the unit-capacity prime/double-prime network.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-to-flow-network"
      ],
      "source_label": "poset reconstruction from its flow network",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:poset-rank",
      "definition": "A level of a graded poset consisting of elements having the same rank value.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order"
      ],
      "source_label": "rank",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_subset-lattice",
        "r012:unit:fig_4cube"
      ]
    },
    {
      "concept_id": "r012:concept:poset-to-flow-network",
      "definition": "Duplicate each poset element into a prime and double-prime vertex and add a unit-capacity middle edge for each strict comparison.",
      "prerequisite_concept_ids": [
        "r012:concept:network-flow",
        "r012:concept:poset"
      ],
      "source_label": "poset to flow-network construction",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_chain-partition"
      ]
    },
    {
      "concept_id": "r012:concept:poset-width",
      "definition": "The maximum cardinality of an antichain in a finite poset.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-antichain"
      ],
      "source_label": "width of a poset",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:thm_dilworth",
        "r012:unit:fig_width7",
        "r012:unit:ch_flowapplications",
        "r012:unit:s_flowapplications_chain-partition"
      ]
    },
    {
      "concept_id": "r012:concept:positional-base-notation",
      "definition": "A representation of nonnegative integers as finite strings of digits selected below a chosen base.",
      "prerequisite_concept_ids": [
        "r012:concept:nonnegative-integer",
        "r012:concept:division-algorithm"
      ],
      "source_label": "positional notation in base b",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_decimal"
      ]
    },
    {
      "concept_id": "r012:concept:positive-cut",
      "definition": "A Dedekind cut representing a positive real number.",
      "prerequisite_concept_ids": [
        "r012:concept:dedekind-cut"
      ],
      "source_label": "positive Dedekind cut",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_reals"
      ]
    },
    {
      "concept_id": "r012:concept:positive-half-binomial-coefficient",
      "definition": "The closed form for binom(1/2,k) used to extract Catalan coefficients from sqrt(1-4x).",
      "prerequisite_concept_ids": [
        "r012:concept:generalized-binomial-coefficient"
      ],
      "source_label": "one-half generalized binomial coefficient",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:l_half-binomial",
        "r012:unit:thm_catalan-genfunction"
      ]
    },
    {
      "concept_id": "r012:concept:positive-integer",
      "definition": "An integer greater than zero.",
      "prerequisite_concept_ids": [],
      "source_label": "positive integer",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_number",
        "r012:unit:s_inclusion-exclusion_euler-phi",
        "r012:unit:thm_eulerphi",
        "r012:unit:prop_num-divisible",
        "r012:unit:s_background_int-union",
        "r012:unit:s_background_finite-sets"
      ]
    },
    {
      "concept_id": "r012:concept:positive-integer-induction",
      "definition": "A subset of positive integers is all positive integers when it contains one and is successor-closed.",
      "prerequisite_concept_ids": [
        "r012:concept:mathematical-induction",
        "r012:concept:positive-integer"
      ],
      "source_label": "induction on positive integers",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_decimal"
      ]
    },
    {
      "concept_id": "r012:concept:postdoctoral-position",
      "definition": "A temporary research appointment held after the doctorate.",
      "prerequisite_concept_ids": [],
      "source_label": "postdoctoral position",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:power-series",
      "definition": "An expression of the form sum from n=0 to infinity of a_n x^n, determined by its coefficient sequence.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence"
      ],
      "source_label": "power series",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:5d06d4ea1ab81098c21c9be0",
        "r012:unit:s_genfunction_intro",
        "r012:unit:exam_genfunction_geom-series",
        "r012:unit:auto:0be40ee4fe111164419b75cb",
        "r012:unit:prop_genfunction-product",
        "r012:unit:s_genfunction_distributions",
        "r012:unit:s_genfunction_gen-bin-thm",
        "r012:unit:thm_newton-binomial",
        "r012:unit:s_genfunction_exponential",
        "r012:unit:auto:a92a089aa7a8dd70c223b7f8"
      ]
    },
    {
      "concept_id": "r012:concept:power-series-product",
      "definition": "The Cauchy product in which the coefficient of x^n is the sum from k=0 to n of a_k b_{n-k}.",
      "prerequisite_concept_ids": [
        "r012:concept:formal-power-series",
        "r012:concept:generating-function"
      ],
      "source_label": "product of power series",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_intro",
        "r012:unit:prop_genfunction-product",
        "r012:unit:s_genfunction_distributions",
        "r012:unit:s_genfunction_binom-app",
        "r012:unit:auto:77bb8e40ef7c0def33263edd",
        "r012:unit:s_genfunction_partitions-integer",
        "r012:unit:thm_partition",
        "r012:unit:auto:c1cbbffbb5bf258ea18be45d",
        "r012:unit:auto:a65033c7e640b8b32155ee76"
      ]
    },
    {
      "concept_id": "r012:concept:power-set-axiom",
      "definition": "Every set has a set containing exactly all of its subsets.",
      "prerequisite_concept_ids": [
        "r012:concept:zfc-set-theory"
      ],
      "source_label": "power-set axiom",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_ZFC"
      ]
    },
    {
      "concept_id": "r012:concept:predicate",
      "definition": "An open statement whose truth value depends on one or more variables.",
      "prerequisite_concept_ids": [],
      "source_label": "predicate",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_intro",
        "r012:unit:s_background_notation"
      ]
    },
    {
      "concept_id": "r012:concept:preference",
      "definition": "A comparison in which one alternative is favored over another.",
      "prerequisite_concept_ids": [],
      "source_label": "preference",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_discussion"
      ]
    },
    {
      "concept_id": "r012:concept:prim-algorithm",
      "definition": "Grow one tree from a root by repeatedly adding a minimum-weight edge leaving the current vertex set.",
      "prerequisite_concept_ids": [
        "r012:concept:safe-minimum-cut-edge"
      ],
      "source_label": "Prim's algorithm",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:alg_prim"
      ]
    },
    {
      "concept_id": "r012:concept:prime-counting-function",
      "definition": "The function pi(n) counting primes not exceeding n.",
      "prerequisite_concept_ids": [
        "r012:concept:number-theory",
        "r012:concept:function"
      ],
      "source_label": "prime-counting function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_exact"
      ]
    },
    {
      "concept_id": "r012:concept:prime-factorization",
      "definition": "Expression of a positive integer as a product of prime powers.",
      "prerequisite_concept_ids": [
        "r012:concept:number-theory"
      ],
      "source_label": "prime factorization",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_number",
        "r012:unit:s_inclusion-exclusion_euler-phi",
        "r012:unit:thm_eulerphi",
        "r012:unit:auto:5cf98fb376a04e75419df1f9",
        "r012:unit:auto:78cd58d5f8395977c731d2e1",
        "r012:unit:s_inclusion-exclusion_discussion"
      ]
    },
    {
      "concept_id": "r012:concept:prime-membership-witness",
      "definition": "A factorization witnesses compositeness, while primality requires a complete justification.",
      "prerequisite_concept_ids": [
        "r012:concept:prime-number",
        "r012:concept:set-membership"
      ],
      "source_label": "witnessing prime membership or nonmembership",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_intro"
      ]
    },
    {
      "concept_id": "r012:concept:prime-number",
      "definition": "A positive integer greater than one whose only positive divisors are one and itself.",
      "prerequisite_concept_ids": [
        "r012:concept:positive-integer"
      ],
      "source_label": "prime number",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_intro"
      ]
    },
    {
      "concept_id": "r012:concept:probabilistic-method",
      "definition": "An existence method that proves a desired object exists by showing a random object has the desired property with positive probability.",
      "prerequisite_concept_ids": [
        "r012:concept:probability-space",
        "r012:concept:expected-value"
      ],
      "source_label": "probabilistic method",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_ramsey_probability",
        "r012:unit:s_ramsey_girth",
        "r012:unit:s_kitchensink_applying-local-lemma"
      ]
    },
    {
      "concept_id": "r012:concept:probability",
      "definition": "A numerical measure of uncertainty assigned to events.",
      "prerequisite_concept_ids": [],
      "source_label": "probability",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_probability"
      ]
    },
    {
      "concept_id": "r012:concept:probability-exercise-synthesis",
      "definition": "Exercises combining counting, complements, conditional probability, expectation, and independence.",
      "prerequisite_concept_ids": [
        "r012:concept:probability",
        "r012:concept:conditional-probability",
        "r012:concept:expected-value"
      ],
      "source_label": "probability exercise synthesis",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:probability-measure",
      "definition": "A normalized finitely additive function assigning values in [0,1] to events.",
      "prerequisite_concept_ids": [
        "r012:concept:probability-space"
      ],
      "source_label": "probability measure",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_intro"
      ]
    },
    {
      "concept_id": "r012:concept:probability-space",
      "definition": "A finite outcome set together with a probability measure on all of its subsets.",
      "prerequisite_concept_ids": [
        "r012:concept:finite-set",
        "r012:concept:set-function"
      ],
      "source_label": "probability space",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_intro",
        "r012:unit:s_ramsey_probability",
        "r012:unit:s_kitchensink_lovasz-local"
      ]
    },
    {
      "concept_id": "r012:concept:proper-coloring",
      "definition": "A vertex coloring in which adjacent vertices receive different colors.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-coloring",
        "r012:concept:adjacency"
      ],
      "source_label": "proper coloring",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_color",
        "r012:unit:disc-graphs_color-intro",
        "r012:unit:graphs_PI_coloring-defn",
        "r012:unit:s_kitchensink_online"
      ]
    },
    {
      "concept_id": "r012:concept:proper-subset",
      "definition": "A subset that omits at least one element of the containing set.",
      "prerequisite_concept_ids": [
        "r012:concept:set-inclusion"
      ],
      "source_label": "proper subset",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_int-union"
      ]
    },
    {
      "concept_id": "r012:concept:proposition",
      "definition": "A declarative statement having a truth value.",
      "prerequisite_concept_ids": [],
      "source_label": "proposition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_notation",
        "r012:unit:s_background_equivalence"
      ]
    },
    {
      "concept_id": "r012:concept:prufer-code",
      "definition": "A length-(n-2) sequence encoding a labeled tree on n vertices by repeatedly deleting the least-labeled leaf and recording its neighbor.",
      "prerequisite_concept_ids": [
        "r012:concept:labeled-tree",
        "r012:concept:sequence",
        "r012:concept:leaf"
      ],
      "source_label": "Prüfer code",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_cayley",
        "r012:unit:ex_prufer-code",
        "r012:unit:ex_prufer-code-reverse"
      ]
    },
    {
      "concept_id": "r012:concept:public-key-cryptography",
      "definition": "Cryptographic methods that use a publicly distributable key together with separate secret information; the discussion highlights the factorization of products of large primes as one important setting.",
      "prerequisite_concept_ids": [],
      "source_label": "public key cryptography",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_inclusion-exclusion_discussion"
      ]
    },
    {
      "concept_id": "r012:concept:quantitative-finance-career",
      "definition": "A finance career centered on intensive analytical problem solving.",
      "prerequisite_concept_ids": [],
      "source_label": "quantitative finance career",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:quick-sort",
      "definition": "A comparison-sorting algorithm that partitions around a pivot and recursively sorts the resulting parts.",
      "prerequisite_concept_ids": [
        "r012:concept:sorting",
        "r012:concept:recursion"
      ],
      "source_label": "quick sort",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_sorting"
      ]
    },
    {
      "concept_id": "r012:concept:radius-of-convergence",
      "definition": "The nonnegative radius R within which a power series converges and beyond which it diverges; R may be zero or infinite.",
      "prerequisite_concept_ids": [
        "r012:concept:power-series"
      ],
      "source_label": "radius of convergence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_intro"
      ]
    },
    {
      "concept_id": "r012:concept:ramsey-event-dependency-count",
      "definition": "Bad events depend exactly when their underlying vertex sets share at least two vertices, yielding explicit neighborhood counts.",
      "prerequisite_concept_ids": [
        "r012:concept:dependency-neighborhood",
        "r012:concept:triangle-bad-event",
        "r012:concept:independent-set-bad-event"
      ],
      "source_label": "Ramsey event dependency count",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_applying-local-lemma"
      ]
    },
    {
      "concept_id": "r012:concept:ramsey-number",
      "definition": "The least graph order forcing either a clique of one prescribed size or an independent set of another prescribed size.",
      "prerequisite_concept_ids": [
        "r012:concept:clique",
        "r012:concept:independent-set"
      ],
      "source_label": "Ramsey number",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probmeth_graph-ramsey",
        "r012:unit:s_ramsey_small",
        "r012:unit:s_kitchensink_applying-local-lemma"
      ]
    },
    {
      "concept_id": "r012:concept:ramsey-property",
      "definition": "A threshold property guaranteeing a clique or an independent set of a prescribed size.",
      "prerequisite_concept_ids": [
        "r012:concept:clique",
        "r012:concept:independent-set"
      ],
      "source_label": "clique-or-independent-set guarantee",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:4f427a0d8cd35dd9d5f9a181",
        "r012:unit:thm_graphramsey",
        "r012:unit:thm_genramsey",
        "r012:unit:s_kitchensink_arithmetic-combinatorics",
        "r012:unit:auto:2c43873e0968cfc6d26f9acb"
      ]
    },
    {
      "concept_id": "r012:concept:random-graph",
      "definition": "A graph generated by a specified probability model.",
      "prerequisite_concept_ids": [
        "r012:concept:graph",
        "r012:concept:probability-space"
      ],
      "source_label": "random graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:6691548129df37fcc64c5423",
        "r012:unit:s_ramsey_probability",
        "r012:unit:s_ramsey_girth",
        "r012:unit:s_ramsey_exercises",
        "r012:unit:s_kitchensink_applying-local-lemma"
      ]
    },
    {
      "concept_id": "r012:concept:random-tournament",
      "definition": "A tournament obtained by independently choosing each edge orientation with equal probability.",
      "prerequisite_concept_ids": [
        "r012:concept:tournament",
        "r012:concept:probability-space"
      ],
      "source_label": "random tournament",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_ramsey_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:random-variable",
      "definition": "A real-valued function on the outcomes of a probability space.",
      "prerequisite_concept_ids": [
        "r012:concept:probability-space",
        "r012:concept:function"
      ],
      "source_label": "random variable",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:fa26c80a67c89c43da03624e",
        "r012:unit:s_ramsey_probability",
        "r012:unit:thm_girth"
      ]
    },
    {
      "concept_id": "r012:concept:rational-arithmetic",
      "definition": "Well-defined arithmetic on fraction representatives using common-denominator addition and componentwise multiplication.",
      "prerequisite_concept_ids": [
        "r012:concept:rational-number",
        "r012:concept:well-defined-operation"
      ],
      "source_label": "rational addition and multiplication",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:rational-cut",
      "definition": "The cut of all rational numbers strictly below a specified rational q.",
      "prerequisite_concept_ids": [
        "r012:concept:dedekind-cut",
        "r012:concept:rational-number"
      ],
      "source_label": "rational cut",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_reals"
      ]
    },
    {
      "concept_id": "r012:concept:rational-number",
      "definition": "An equivalence class represented by an integer numerator and nonzero integer denominator.",
      "prerequisite_concept_ids": [
        "r012:concept:rational-pair-equivalence",
        "r012:concept:equivalence-class"
      ],
      "source_label": "rational number",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:rational-order",
      "definition": "For positive denominators, (a,b) is at most (c,d) when ad is at most bc.",
      "prerequisite_concept_ids": [
        "r012:concept:rational-number",
        "r012:concept:integer-total-order"
      ],
      "source_label": "total order on the rationals",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:rational-pair-equivalence",
      "definition": "Integer pairs (x,y) and (z,w), with nonzero denominators, are equivalent when xw=yz.",
      "prerequisite_concept_ids": [
        "r012:concept:integer",
        "r012:concept:equivalence-relation"
      ],
      "source_label": "fraction-pair equivalence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_rationals"
      ]
    },
    {
      "concept_id": "r012:concept:real-number-as-cut",
      "definition": "A real number represented by a Dedekind cut of the rationals.",
      "prerequisite_concept_ids": [
        "r012:concept:dedekind-cut"
      ],
      "source_label": "real number as a cut",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_reals"
      ]
    },
    {
      "concept_id": "r012:concept:real-vector-space",
      "definition": "A set of vectors equipped with addition and real scalar multiplication satisfying the eight listed vector-space axioms.",
      "prerequisite_concept_ids": [],
      "source_label": "vector space over the real numbers",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:ba2f054b693f6319b15736f2"
      ]
    },
    {
      "concept_id": "r012:concept:receiver-monotonicity",
      "definition": "The receiver retained by each seller weakly improves throughout deferred acceptance.",
      "prerequisite_concept_ids": [
        "r012:concept:deferred-acceptance-algorithm"
      ],
      "source_label": "receiver-side monotonicity",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_stable-match"
      ]
    },
    {
      "concept_id": "r012:concept:recurrence",
      "definition": "A rule that specifies later terms or function values from earlier ones, together with enough initial values to determine the sequence.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence"
      ],
      "source_label": "recurrence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_recurrence",
        "r012:unit:auto:b2a4979434434bc7233ca327",
        "r012:unit:s_recurrence_intro",
        "r012:unit:s_recurrence_intro_fib",
        "r012:unit:auto:a5fd615b1106d334b47d57d4",
        "r012:unit:s_recurrence_intro_strings",
        "r012:unit:ex_recurrence_binary-strings-no-11",
        "r012:unit:ex_recurrence_ternary-strings-no-20",
        "r012:unit:s_recurrence_intro_lines",
        "r012:unit:s_recurrence_solving",
        "r012:unit:s_recurrence_solving_homogeneous",
        "r012:unit:s_recurrence_solving_nonhomogeneous"
      ]
    },
    {
      "concept_id": "r012:concept:recurrence-equation",
      "definition": "An equation expressing a sequence term or function value in terms of preceding terms or values.",
      "prerequisite_concept_ids": [
        "r012:concept:recurrence"
      ],
      "source_label": "recurrence equation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_recurrence",
        "r012:unit:auto:b2a4979434434bc7233ca327",
        "r012:unit:s_recurrence_intro",
        "r012:unit:s_recurrence_solving",
        "r012:unit:ex_recurrence_deg2",
        "r012:unit:ex_recurrence_ternary-strings-no-20-solved",
        "r012:unit:ex_recurrence_deg4-repeated",
        "r012:unit:s_recurrence_solving_nonhomogeneous",
        "r012:unit:ex_recurrence_lines-solved",
        "r012:unit:rqs-recurrence_solving"
      ]
    },
    {
      "concept_id": "r012:concept:recurrence-equation-exercise-synthesis",
      "definition": "Integrated practice deriving, classifying, and solving recurrence equations with varied initial data.",
      "prerequisite_concept_ids": [
        "r012:concept:recurrence-relation",
        "r012:concept:linear-recurrence-equation"
      ],
      "source_label": "recurrence equation exercise synthesis",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:recurrence-generating-function-exercise-synthesis",
      "definition": "Practice solving homogeneous and nonhomogeneous recurrences through generating functions and extracting closed forms.",
      "prerequisite_concept_ids": [
        "r012:concept:generating-function-recurrence-method"
      ],
      "source_label": "generating-function exercise synthesis for recurrences",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ex_recurrence_gen-fn",
        "r012:unit:auto:fdcb4e382775725188f7ddfb",
        "r012:unit:auto:8b87a353e8228ac6d2ab68b5",
        "r012:unit:auto:3110fa2523dd10b3fb16b771"
      ]
    },
    {
      "concept_id": "r012:concept:recurrence-relation",
      "definition": "A relation expressing sequence terms through earlier terms.",
      "prerequisite_concept_ids": [
        "r012:concept:enumeration"
      ],
      "source_label": "recurrence relation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:s_recurrence_adv-ops",
        "r012:unit:ex_recurrence_adveq",
        "r012:unit:s_recurrence_adv-ops_const-coeff",
        "r012:unit:rqs-recurrence_adv-ops",
        "r012:unit:rq-recurrence_adv-ops_rewrite"
      ]
    },
    {
      "concept_id": "r012:concept:recurrence-runtime-benchmark",
      "definition": "An empirical timing comparison between direct recursion and a mathematically equivalent explicit formula.",
      "prerequisite_concept_ids": [
        "r012:concept:recursive-evaluation",
        "r012:concept:explicit-recurrence-solution"
      ],
      "source_label": "runtime comparison of recursive and explicit recurrence evaluation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_discussion",
        "r012:unit:recurrence_discussion_takeaways"
      ]
    },
    {
      "concept_id": "r012:concept:recursion",
      "definition": "The specification or computation of an object in terms of smaller instances of the same kind.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence"
      ],
      "source_label": "recursion",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_induction"
      ]
    },
    {
      "concept_id": "r012:concept:recursive-addition",
      "definition": "Addition on natural numbers defined by n+0=n and n+s(k)=s(n+k).",
      "prerequisite_concept_ids": [
        "r012:concept:successor-function",
        "r012:concept:mathematical-induction"
      ],
      "source_label": "formal recursive definition of addition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_add",
        "r012:unit:s_background_formal-num-sys"
      ]
    },
    {
      "concept_id": "r012:concept:recursive-evaluation",
      "definition": "Direct computation of a sequence value by recursively invoking earlier sequence values.",
      "prerequisite_concept_ids": [
        "r012:concept:recursion",
        "r012:concept:recurrence-relation"
      ],
      "source_label": "recursive evaluation of a recurrence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_discussion"
      ]
    },
    {
      "concept_id": "r012:concept:recursive-multiplication",
      "definition": "Multiplication on natural numbers defined by n0=0 and n(k+1)=nk+n.",
      "prerequisite_concept_ids": [
        "r012:concept:recursive-addition"
      ],
      "source_label": "formal recursive definition of multiplication",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_mult"
      ]
    },
    {
      "concept_id": "r012:concept:reflection",
      "definition": "A symmetry transformation that reverses orientation across an axis or mirror line.",
      "prerequisite_concept_ids": [
        "r012:concept:group-action"
      ],
      "source_label": "reflection",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_square"
      ]
    },
    {
      "concept_id": "r012:concept:reflexive-relation",
      "definition": "A relation on X is reflexive when every x in X is related to itself.",
      "prerequisite_concept_ids": [
        "r012:concept:binary-relation"
      ],
      "source_label": "reflexive binary relation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_order",
        "r012:unit:s_background_equivalence",
        "r012:unit:s_background_integers"
      ]
    },
    {
      "concept_id": "r012:concept:regular-graph",
      "definition": "A graph in which every vertex has the same degree.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "regular graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_polya"
      ]
    },
    {
      "concept_id": "r012:concept:regular-transition-matrix",
      "definition": "A transition matrix for which some positive power has only positive entries.",
      "prerequisite_concept_ids": [
        "r012:concept:transition-matrix"
      ],
      "source_label": "regular transition matrix",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_regular",
        "r012:unit:s_kitchensink_markov-chains"
      ]
    },
    {
      "concept_id": "r012:concept:regularity-axiom",
      "definition": "Every nonempty set has an element disjoint from it.",
      "prerequisite_concept_ids": [
        "r012:concept:zfc-set-theory"
      ],
      "source_label": "axiom of regularity",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_ZFC"
      ]
    },
    {
      "concept_id": "r012:concept:relative-primality",
      "definition": "Two integers are relatively prime when their greatest common divisor is 1.",
      "prerequisite_concept_ids": [
        "r012:concept:greatest-common-divisor"
      ],
      "source_label": "relatively prime",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_inclusion-exclusion_euler-phi",
        "r012:unit:inclusion-exclusion_PI_rel-prime"
      ]
    },
    {
      "concept_id": "r012:concept:repeated-independent-sampling",
      "definition": "Repeated draws from one probability space in which each draw is independent of the preceding draws.",
      "prerequisite_concept_ids": [
        "r012:concept:independent-events",
        "r012:concept:probability-space"
      ],
      "source_label": "repeated independent sampling",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:9f5b75658465146534f073d6"
      ]
    },
    {
      "concept_id": "r012:concept:repeated-root-recurrence-solution",
      "definition": "A root r of multiplicity k contributes the k independent solution forms r^n, nr^n, through n^(k-1)r^n.",
      "prerequisite_concept_ids": [
        "r012:concept:distinct-root-recurrence-solution"
      ],
      "source_label": "repeated-root solution of a homogeneous recurrence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rigorous_repeated",
        "r012:unit:lem_rr",
        "r012:unit:eqn_rr",
        "r012:unit:eqn_solutionrr",
        "r012:unit:ex_recurrence_deg2-repeated",
        "r012:unit:ex_recurrence_deg4-repeated"
      ]
    },
    {
      "concept_id": "r012:concept:repeating-decimal",
      "definition": "A decimal expansion with a finite block of digits that repeats indefinitely.",
      "prerequisite_concept_ids": [
        "r012:concept:decimal-expansion",
        "r012:concept:rational-number"
      ],
      "source_label": "repeating decimal",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_complex"
      ]
    },
    {
      "concept_id": "r012:concept:replacement-axiom",
      "definition": "The image of a set under a definable functional rule is a set.",
      "prerequisite_concept_ids": [
        "r012:concept:zfc-set-theory"
      ],
      "source_label": "axiom schema of replacement",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_ZFC"
      ]
    },
    {
      "concept_id": "r012:concept:required-symbol-egf-factor",
      "definition": "The factor e^x-1, or a corresponding truncated exponential series, used to require one or more occurrences of a symbol.",
      "prerequisite_concept_ids": [
        "r012:concept:exponential-generating-function"
      ],
      "source_label": "required-symbol exponential generating-function factor",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:3259ae9833c0290eb6d05545",
        "r012:unit:auto:4b9b577c7e32e0494cb91c36",
        "r012:unit:ex_genfunction_exponential_passcode",
        "r012:unit:rqs-genfunction_exponential",
        "r012:unit:rq-genfunction_exponential_passcode",
        "r012:unit:auto:cd91522cddb9cb10442a7836",
        "r012:unit:auto:f3edcd631926927e1e6b9719",
        "r012:unit:auto:fdf77306cd6d226cfda10c55",
        "r012:unit:auto:39ab9828f6c93359abfbc514",
        "r012:unit:genfunction_PI_string-restrict-4",
        "r012:unit:genfunction_PI_string-restrict-2"
      ]
    },
    {
      "concept_id": "r012:concept:restricted-exponentiation",
      "definition": "A two-argument natural-number operation defined on all pairs except (0,0), recursively in the exponent.",
      "prerequisite_concept_ids": [
        "r012:concept:recursive-multiplication"
      ],
      "source_label": "exponentiation excluding 0^0",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_exp"
      ]
    },
    {
      "concept_id": "r012:concept:restricted-object-distribution",
      "definition": "A distribution problem whose recipient or object-type counts obey lower bounds, upper bounds, parity, congruence, or other allowed-value restrictions.",
      "prerequisite_concept_ids": [
        "r012:concept:generating-function-distribution-model"
      ],
      "source_label": "restricted distribution of objects",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_distributions",
        "r012:unit:exa_genfunction_apples",
        "r012:unit:exa_genfunction_fruit",
        "r012:unit:auto:2d043fada756b0e678fbcfa4",
        "r012:unit:exa_genfunction_partial-fracs",
        "r012:unit:auto:692d3d5206064b390fb35ace",
        "r012:unit:rqs-genfunction_distributions",
        "r012:unit:genfunction_distributions_rq-constant_term",
        "r012:unit:genfunction_distributions_rq-coins",
        "r012:unit:auto:e1321354951ba5fcec2ae15c",
        "r012:unit:auto:ad5800950b29d7f51c43a73e",
        "r012:unit:ex_genfunction_ineq-clean",
        "r012:unit:auto:6b0d982902d4e6cfc0dfed45",
        "r012:unit:auto:318098a808461c4b431eaeec",
        "r012:unit:auto:9da8ebe78f63c221b5b6bc64",
        "r012:unit:auto:8def6d29b55112ab987c47ed",
        "r012:unit:ex_genfunction_ineq-messy",
        "r012:unit:genfunction_PI_apples-one",
        "r012:unit:genfunction_PI_apples-five",
        "r012:unit:genfunction_PI_apples-oranges-bananas",
        "r012:unit:genfunction_PI_polynomial"
      ]
    },
    {
      "concept_id": "r012:concept:restricted-passcode-egf",
      "definition": "A product of exponential-series factors encoding independent parity, lower-bound, and upper-bound restrictions on passcode digits.",
      "prerequisite_concept_ids": [
        "r012:concept:exponential-generating-function",
        "r012:concept:even-symbol-count-filter",
        "r012:concept:required-symbol-egf-factor"
      ],
      "source_label": "exponential generating function for restricted passcodes",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ex_genfunction_exponential_passcode",
        "r012:unit:rqs-genfunction_exponential",
        "r012:unit:rq-genfunction_exponential_passcode"
      ]
    },
    {
      "concept_id": "r012:concept:right-child",
      "definition": "The second of the two ordered children at an internal RUBOT vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:ordered-tree",
        "r012:concept:tree-child"
      ],
      "source_label": "right child",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots"
      ]
    },
    {
      "concept_id": "r012:concept:root-vertex",
      "definition": "A designated vertex from which a graph construction or path computation begins.",
      "prerequisite_concept_ids": [
        "r012:concept:vertex"
      ],
      "source_label": "root vertex",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_graphalgorithms"
      ]
    },
    {
      "concept_id": "r012:concept:rooted-tree",
      "definition": "A tree with one designated vertex called its root.",
      "prerequisite_concept_ids": [
        "r012:concept:tree",
        "r012:concept:vertex"
      ],
      "source_label": "rooted tree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots"
      ]
    },
    {
      "concept_id": "r012:concept:row-column-sum-strings",
      "definition": "The ordered row totals and column totals of a zero-one matrix.",
      "prerequisite_concept_ids": [
        "r012:concept:zero-one-matrix"
      ],
      "source_label": "row and column sum strings",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_zero-one-matrices"
      ]
    },
    {
      "concept_id": "r012:concept:rubot",
      "definition": "A rooted, unlabeled, full binary, ordered tree, abbreviated RUBOT.",
      "prerequisite_concept_ids": [
        "r012:concept:rooted-tree",
        "r012:concept:unlabeled-tree",
        "r012:concept:full-binary-tree",
        "r012:concept:ordered-tree"
      ],
      "source_label": "rooted unlabeled binary ordered tree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots",
        "r012:unit:fig_rubots",
        "r012:unit:thm_catalan-genfunction"
      ]
    },
    {
      "concept_id": "r012:concept:rubot-catalan-recurrence",
      "definition": "The decomposition of a RUBOT at its ordered left and right subtrees, giving c_n=sum from k=0 to n of c_k c_(n-k) for n at least 2 with c_0=0 and c_1=1.",
      "prerequisite_concept_ids": [
        "r012:concept:rubot",
        "r012:concept:recurrence-relation"
      ],
      "source_label": "Catalan recurrence for RUBOTs",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots"
      ]
    },
    {
      "concept_id": "r012:concept:rubot-generating-function",
      "definition": "The Catalan generating function C(x)=(1-sqrt(1-4x))/2 whose x^n coefficient counts RUBOTs with n leaves.",
      "prerequisite_concept_ids": [
        "r012:concept:rubot-catalan-recurrence",
        "r012:concept:generating-function",
        "r012:concept:generalized-binomial-theorem"
      ],
      "source_label": "generating function for RUBOTs",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots",
        "r012:unit:thm_catalan-genfunction"
      ]
    },
    {
      "concept_id": "r012:concept:safe-minimum-cut-edge",
      "definition": "A minimum-weight edge leaving a current forest component belongs to some minimum-weight spanning tree extending that forest.",
      "prerequisite_concept_ids": [
        "r012:concept:spanning-tree-exchange-principle"
      ],
      "source_label": "minimum edge leaving a forest component",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:lem_graphalgorithms_tech"
      ]
    },
    {
      "concept_id": "r012:concept:safety-net",
      "definition": "An institutional protective system supporting public security and well-being.",
      "prerequisite_concept_ids": [
        "r012:concept:computational-public-health"
      ],
      "source_label": "safety net",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:sage-power-series-expansion",
      "definition": "Use of SageMath series and coefficient-list operations to expand a generating function and extract selected coefficients.",
      "prerequisite_concept_ids": [
        "r012:concept:power-series",
        "r012:concept:partial-fraction-coefficient-extraction"
      ],
      "source_label": "SageMath power-series expansion",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_genfunction_distributions",
        "r012:unit:auto:692d3d5206064b390fb35ace",
        "r012:unit:ex_genfunction_exponential_passcode"
      ]
    },
    {
      "concept_id": "r012:concept:sample-space",
      "definition": "The set of all outcomes of an experiment.",
      "prerequisite_concept_ids": [],
      "source_label": "sample space",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_intro"
      ]
    },
    {
      "concept_id": "r012:concept:sampling-without-replacement",
      "definition": "Random selection in which selected objects are not returned before later selections.",
      "prerequisite_concept_ids": [
        "r012:concept:probability"
      ],
      "source_label": "sampling without replacement",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:d275dcdb8b05d03219dfcac9"
      ]
    },
    {
      "concept_id": "r012:concept:scale",
      "definition": "An ordered collection of pitches or pitch classes used as a tonal framework.",
      "prerequisite_concept_ids": [],
      "source_label": "musical scale",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:scale-transposition",
      "definition": "Uniform addition modulo twelve to every pitch class in a scale.",
      "prerequisite_concept_ids": [
        "r012:concept:cyclic-group",
        "r012:concept:modular-arithmetic"
      ],
      "source_label": "scale transposition",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:scheduling-irregularity",
      "definition": "A disruption requiring changes to an operating schedule.",
      "prerequisite_concept_ids": [
        "r012:concept:industrial-optimization"
      ],
      "source_label": "scheduling irregularity",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:second-coordinate",
      "definition": "The second component of an ordered pair.",
      "prerequisite_concept_ids": [
        "r012:concept:ordered-pair"
      ],
      "source_label": "second coordinate",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_products"
      ]
    },
    {
      "concept_id": "r012:concept:self-dual-poset",
      "definition": "A poset isomorphic to its dual.",
      "prerequisite_concept_ids": [
        "r012:concept:dual-poset",
        "r012:concept:poset-isomorphism"
      ],
      "source_label": "self-dual poset",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:separation-axiom",
      "definition": "A definable subclass of a set is itself a set.",
      "prerequisite_concept_ids": [
        "r012:concept:zfc-set-theory"
      ],
      "source_label": "axiom schema of separation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_ZFC"
      ]
    },
    {
      "concept_id": "r012:concept:sequence",
      "definition": "An ordered list of mathematical objects indexed by position.",
      "prerequisite_concept_ids": [],
      "source_label": "sequence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ex_collatz",
        "r012:unit:thm_ErdosSzekeres",
        "r012:unit:s_recurrence_intro_fib",
        "r012:unit:tab_fib-ratios",
        "r012:unit:auto:12b6629772d99bdcaab15a9b",
        "r012:unit:ex_recurrence_adveq"
      ]
    },
    {
      "concept_id": "r012:concept:set",
      "definition": "A collection whose membership is unambiguous for every candidate element.",
      "prerequisite_concept_ids": [],
      "source_label": "set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_intro"
      ]
    },
    {
      "concept_id": "r012:concept:set-builder-notation",
      "definition": "Notation defining a set through a membership rule rather than an explicit list.",
      "prerequisite_concept_ids": [
        "r012:concept:set",
        "r012:concept:predicate"
      ],
      "source_label": "set-builder notation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_intro"
      ]
    },
    {
      "concept_id": "r012:concept:set-equality-criterion",
      "definition": "Two sets are equal exactly when each is a subset of the other.",
      "prerequisite_concept_ids": [
        "r012:concept:set-inclusion"
      ],
      "source_label": "equality of sets",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_int-union"
      ]
    },
    {
      "concept_id": "r012:concept:set-family",
      "definition": "A collection of sets considered as one mathematical object.",
      "prerequisite_concept_ids": [],
      "source_label": "set family",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_extremal-set-theory"
      ]
    },
    {
      "concept_id": "r012:concept:set-function",
      "definition": "A function whose arguments are sets.",
      "prerequisite_concept_ids": [
        "r012:concept:function"
      ],
      "source_label": "set function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_intro"
      ]
    },
    {
      "concept_id": "r012:concept:set-inclusion",
      "definition": "The partial order in which one set precedes another exactly when it is a subset of the other.",
      "prerequisite_concept_ids": [
        "r012:concept:set-membership",
        "r012:concept:partial-order"
      ],
      "source_label": "set inclusion",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:s_posets_subset-lattice",
        "r012:unit:s_background_int-union",
        "r012:unit:s_background_relations"
      ]
    },
    {
      "concept_id": "r012:concept:set-intersection",
      "definition": "The set of elements belonging to both given sets.",
      "prerequisite_concept_ids": [
        "r012:concept:set-membership"
      ],
      "source_label": "set intersection",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_int-union"
      ]
    },
    {
      "concept_id": "r012:concept:set-membership",
      "definition": "The relation in which a specified object is an element of a set.",
      "prerequisite_concept_ids": [
        "r012:concept:set"
      ],
      "source_label": "contain",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:induction_PI_subsets-contain-1",
        "r012:unit:s_background_intro",
        "r012:unit:s_background_int-union",
        "r012:unit:s_background_relations",
        "r012:unit:s_background_finite-sets"
      ]
    },
    {
      "concept_id": "r012:concept:set-partition",
      "definition": "A family of pairwise disjoint subsets whose union is the original set.",
      "prerequisite_concept_ids": [
        "r012:concept:pairwise-disjoint"
      ],
      "source_label": "partition of a set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_enum",
        "r012:unit:s_background_equivalence"
      ]
    },
    {
      "concept_id": "r012:concept:set-theoretic-foundations",
      "definition": "An axiomatic framework in which mathematical objects and number systems are constructed from sets.",
      "prerequisite_concept_ids": [],
      "source_label": "set-theoretic foundations",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:app_background",
        "r012:unit:s_background_ZFC"
      ]
    },
    {
      "concept_id": "r012:concept:set-union",
      "definition": "The set of elements belonging to at least one of the given sets.",
      "prerequisite_concept_ids": [
        "r012:concept:set-membership"
      ],
      "source_label": "set union",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_int-union"
      ]
    },
    {
      "concept_id": "r012:concept:shortest-path",
      "definition": "A path of minimum total weight between specified vertices.",
      "prerequisite_concept_ids": [
        "r012:concept:path",
        "r012:concept:weighted-graph",
        "r012:concept:optimization"
      ],
      "source_label": "shortest path",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_opt"
      ]
    },
    {
      "concept_id": "r012:concept:shortest-path-algorithm-history",
      "definition": "The publication lineage connecting Moore's equivalent form and Dijkstra's shortest-path algorithm.",
      "prerequisite_concept_ids": [
        "r012:concept:dijkstra-algorithm"
      ],
      "source_label": "history of shortest-path algorithms",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_historical-notes"
      ]
    },
    {
      "concept_id": "r012:concept:shortest-path-subpath-optimality",
      "definition": "Every prefix and suffix cut at an internal vertex of a shortest path is itself shortest between its endpoints.",
      "prerequisite_concept_ids": [
        "r012:concept:directed-distance"
      ],
      "source_label": "subpaths of a shortest path",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_shortest-paths"
      ]
    },
    {
      "concept_id": "r012:concept:simple-graph",
      "definition": "A graph with neither loops nor multiple edges.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "simple graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_multigraphs"
      ]
    },
    {
      "concept_id": "r012:concept:smartphone",
      "definition": "A compact mobile computing and communication device.",
      "prerequisite_concept_ids": [
        "r012:concept:computing-device"
      ],
      "source_label": "smart phone",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:sorting",
      "definition": "The task of rearranging a sequence into a prescribed order.",
      "prerequisite_concept_ids": [
        "r012:concept:sequence"
      ],
      "source_label": "sorting",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_recursion_sorting",
        "r012:unit:s_posets_sorting"
      ]
    },
    {
      "concept_id": "r012:concept:spanning-forest",
      "definition": "A spanning subgraph that is a forest.",
      "prerequisite_concept_ids": [
        "r012:concept:forest",
        "r012:concept:spanning-subgraph"
      ],
      "source_label": "spanning forest",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_min-wt-span"
      ]
    },
    {
      "concept_id": "r012:concept:spanning-forest-component-count",
      "definition": "A spanning forest on n vertices with n-k edges has exactly k components.",
      "prerequisite_concept_ids": [
        "r012:concept:spanning-forest"
      ],
      "source_label": "component count in a spanning forest",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:prop_graphalgorithms_spanforest"
      ]
    },
    {
      "concept_id": "r012:concept:spanning-subgraph",
      "definition": "A subgraph having the same vertex set as the original graph.",
      "prerequisite_concept_ids": [
        "r012:concept:subgraph"
      ],
      "source_label": "spanning subgraph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro",
        "r012:unit:fig_subgraphs"
      ]
    },
    {
      "concept_id": "r012:concept:spanning-tree",
      "definition": "A tree subgraph containing every vertex of the original connected graph.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "spanning tree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro"
      ]
    },
    {
      "concept_id": "r012:concept:spanning-tree-exchange-principle",
      "definition": "Adding a non-tree edge creates one cycle, and deleting any tree edge on that cycle yields another spanning tree.",
      "prerequisite_concept_ids": [
        "r012:concept:spanning-tree"
      ],
      "source_label": "exchange principle",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:prop_graphalgorithms_exchange"
      ]
    },
    {
      "concept_id": "r012:concept:spare-capacity",
      "definition": "The difference c(e)-phi(e) available for increasing flow on a directed edge.",
      "prerequisite_concept_ids": [
        "r012:concept:edge-flow-status"
      ],
      "source_label": "spare capacity",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_augmenting"
      ]
    },
    {
      "concept_id": "r012:concept:sperner-extremal-family",
      "definition": "A maximum antichain in the Boolean lattice consists of a middle rank.",
      "prerequisite_concept_ids": [
        "r012:concept:sperner-theorem"
      ],
      "source_label": "Sperner extremal family",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:exa_Sperner"
      ]
    },
    {
      "concept_id": "r012:concept:sperner-theorem",
      "definition": "The width of the subset lattice on a t-element set equals its largest rank, the middle binomial coefficient.",
      "prerequisite_concept_ids": [
        "r012:concept:subset-lattice",
        "r012:concept:poset-width",
        "r012:concept:binomial-coefficient"
      ],
      "source_label": "Sperner's theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_sperner",
        "r012:unit:s_kitchensink_extremal-set-theory"
      ]
    },
    {
      "concept_id": "r012:concept:square-vertex-coloring",
      "definition": "An assignment of colors to the four labeled vertices of a square.",
      "prerequisite_concept_ids": [
        "r012:concept:finite-coloring"
      ],
      "source_label": "vertex coloring of a square",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_square"
      ]
    },
    {
      "concept_id": "r012:concept:stabilizer",
      "definition": "The subgroup of elements that fix a specified object.",
      "prerequisite_concept_ids": [
        "r012:concept:group-action",
        "r012:concept:fixed-set"
      ],
      "source_label": "stabilizer",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_burnside"
      ]
    },
    {
      "concept_id": "r012:concept:stable-matching",
      "definition": "A one-to-one matching with no buyer-seller pair who prefer each other to their assigned partners.",
      "prerequisite_concept_ids": [
        "r012:concept:matching"
      ],
      "source_label": "stable matching",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_stable-match"
      ]
    },
    {
      "concept_id": "r012:concept:standard-deviation",
      "definition": "The nonnegative square root of the variance.",
      "prerequisite_concept_ids": [
        "r012:concept:variance"
      ],
      "source_label": "standard deviation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:dd704af3675a6c3b2f7eb811"
      ]
    },
    {
      "concept_id": "r012:concept:stationary-limiting-distribution",
      "definition": "A positive probability row vector W with WP=W to which every row of P^m converges for regular P.",
      "prerequisite_concept_ids": [
        "r012:concept:regular-transition-matrix"
      ],
      "source_label": "stationary limiting distribution",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_regular",
        "r012:unit:s_kitchensink_markov-chains"
      ]
    },
    {
      "concept_id": "r012:concept:stirling-approximation",
      "definition": "An asymptotic expansion for n! led by sqrt(2 pi n)(n/e)^n.",
      "prerequisite_concept_ids": [
        "r012:concept:factorial"
      ],
      "source_label": "Stirling approximation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_ramsey_estimatesize"
      ]
    },
    {
      "concept_id": "r012:concept:stochastic-matrix",
      "definition": "A nonnegative matrix whose entries in each row sum to one.",
      "prerequisite_concept_ids": [],
      "source_label": "stochastic matrix",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_markov-chains"
      ]
    },
    {
      "concept_id": "r012:concept:strict-order-from-partial-order",
      "definition": "The relation x<y defined by x≤y together with x≠y.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order"
      ],
      "source_label": "strict order induced by a partial order",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_order"
      ]
    },
    {
      "concept_id": "r012:concept:strict-preference-order",
      "definition": "A ranking without ties that orders all available alternatives by preference.",
      "prerequisite_concept_ids": [],
      "source_label": "strict preference order",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_stable-match"
      ]
    },
    {
      "concept_id": "r012:concept:string",
      "definition": "A finite ordered sequence of symbols.",
      "prerequisite_concept_ids": [
        "r012:concept:discrete-structures"
      ],
      "source_label": "string",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_intro",
        "r012:unit:s_strings_intro",
        "r012:unit:s_strings_permutations",
        "r012:unit:s_strings_combinations",
        "r012:unit:auto:ead8b23e16dc2a353a7c3c9a",
        "r012:unit:s_genfunction_exponential",
        "r012:unit:auto:a92a089aa7a8dd70c223b7f8",
        "r012:unit:auto:7db46e9144887cfe4587f1aa",
        "r012:unit:auto:3259ae9833c0290eb6d05545",
        "r012:unit:auto:4b9b577c7e32e0494cb91c36",
        "r012:unit:ex_genfunction_exponential_passcode",
        "r012:unit:rqs-genfunction_exponential",
        "r012:unit:rq-genfunction_exponential_passcode",
        "r012:unit:auto:cd91522cddb9cb10442a7836",
        "r012:unit:auto:f3edcd631926927e1e6b9719",
        "r012:unit:auto:fdf77306cd6d226cfda10c55",
        "r012:unit:auto:39ab9828f6c93359abfbc514",
        "r012:unit:genfunction_PI_string-restrict-4",
        "r012:unit:genfunction_PI_string-restrict-2",
        "r012:unit:s_recurrence_intro_strings",
        "r012:unit:ex_recurrence_binary-strings-no-11",
        "r012:unit:ex_recurrence_ternary-strings-no-20",
        "r012:unit:ex_recurrence_ternary-strings-no-20-solved"
      ]
    },
    {
      "concept_id": "r012:concept:strong-induction",
      "definition": "An induction principle whose inductive step may assume every preceding instance through the current index.",
      "prerequisite_concept_ids": [
        "r012:concept:mathematical-induction",
        "r012:concept:open-statement"
      ],
      "source_label": "strong induction",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_strong-induction"
      ]
    },
    {
      "concept_id": "r012:concept:subgraph",
      "definition": "A graph whose vertex set and edge set are subsets of those of another graph, with endpoints preserved.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "subgraph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro",
        "r012:unit:fig_subgraphs"
      ]
    },
    {
      "concept_id": "r012:concept:subposet",
      "definition": "A subset equipped with the partial order induced from its containing poset.",
      "prerequisite_concept_ids": [
        "r012:concept:poset",
        "r012:concept:partial-order"
      ],
      "source_label": "subposet",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:s_posets_additional-concepts"
      ]
    },
    {
      "concept_id": "r012:concept:subset-lattice",
      "definition": "The lattice of all subsets of a finite ground set ordered by inclusion.",
      "prerequisite_concept_ids": [
        "r012:concept:lattice",
        "r012:concept:set-inclusion"
      ],
      "source_label": "subset lattice",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_subset-lattice",
        "r012:unit:fig_4cube"
      ]
    },
    {
      "concept_id": "r012:concept:subset-sum",
      "definition": "The decision problem of whether a subset has a prescribed sum.",
      "prerequisite_concept_ids": [
        "r012:concept:computational-complexity"
      ],
      "source_label": "subset sum",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_basics_complexity",
        "r012:unit:s_basics_questions"
      ]
    },
    {
      "concept_id": "r012:concept:substring",
      "definition": "A contiguous block of characters occurring inside a string.",
      "prerequisite_concept_ids": [
        "r012:concept:string"
      ],
      "source_label": "substring",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_intro_strings",
        "r012:unit:ex_recurrence_binary-strings-no-11",
        "r012:unit:ex_recurrence_ternary-strings-no-20"
      ]
    },
    {
      "concept_id": "r012:concept:subtraction",
      "definition": "Addition of an additive inverse.",
      "prerequisite_concept_ids": [
        "r012:concept:additive-inverse"
      ],
      "source_label": "subtraction",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_prop-integers"
      ]
    },
    {
      "concept_id": "r012:concept:success",
      "definition": "The designated favorable outcome of a Bernoulli trial.",
      "prerequisite_concept_ids": [
        "r012:concept:bernoulli-trials"
      ],
      "source_label": "success",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_bernoulli-trials"
      ]
    },
    {
      "concept_id": "r012:concept:successor-function",
      "definition": "The injective map sending each natural number to its successor.",
      "prerequisite_concept_ids": [
        "r012:concept:peano-postulates",
        "r012:concept:injection"
      ],
      "source_label": "successor function",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_formal-num-sys"
      ]
    },
    {
      "concept_id": "r012:concept:sudoku",
      "definition": "A constrained 9 by 9 symbol-placement puzzle with row, column, and 3 by 3 subsquare uniqueness requirements.",
      "prerequisite_concept_ids": [
        "r012:concept:combinatorics"
      ],
      "source_label": "Sudoku puzzle",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_sudoku",
        "r012:unit:fig_sudoku"
      ]
    },
    {
      "concept_id": "r012:concept:surjection",
      "definition": "A function whose range contains every element of its codomain.",
      "prerequisite_concept_ids": [
        "r012:concept:function"
      ],
      "source_label": "surjection",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_inclusion-exclusion",
        "r012:unit:exa_inclusion-exclusion_prop-inject",
        "r012:unit:s_inclusion-exclusion_surjections",
        "r012:unit:auto:d82b928b4ab1bfb15c849fb5",
        "r012:unit:inclusion-exclusion_PI_surjection",
        "r012:unit:s_inclusion-exclusion_surjections_activity",
        "r012:unit:def-surjection",
        "r012:unit:inclusion-exclusion_activity_surjection",
        "r012:unit:s_background_relations",
        "r012:unit:s_background_finite-sets",
        "r012:unit:s_background_complex"
      ]
    },
    {
      "concept_id": "r012:concept:surjection-enumeration-formula",
      "definition": "The inclusion-exclusion formula S(n,m)=sum from k=0 to m of (-1)^k binom(m,k)(m-k)^n for the number of surjections from [n] to [m].",
      "prerequisite_concept_ids": [
        "r012:concept:surjection",
        "r012:concept:inclusion-exclusion"
      ],
      "source_label": "surjection enumeration formula",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_inclusion-exclusion_surjections",
        "r012:unit:auto:d82b928b4ab1bfb15c849fb5",
        "r012:unit:s_inclusion-exclusion_surjections_activity",
        "r012:unit:act_inclusion-exclusion_surjections-formula_conclusion"
      ]
    },
    {
      "concept_id": "r012:concept:symmetric-group",
      "definition": "The group of all permutations of a finite set.",
      "prerequisite_concept_ids": [
        "r012:concept:permutation-group"
      ],
      "source_label": "symmetric group",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_perm-groups"
      ]
    },
    {
      "concept_id": "r012:concept:symmetric-lovasz-local-lemma",
      "definition": "Uniform event-probability and dependency-degree bounds imply simultaneous avoidance under ep(d+1)<1.",
      "prerequisite_concept_ids": [
        "r012:concept:asymmetric-lovasz-local-lemma"
      ],
      "source_label": "symmetric Lovász Local Lemma",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:lem_LLL-sym",
        "r012:unit:s_kitchensink_lovasz-local"
      ]
    },
    {
      "concept_id": "r012:concept:symmetric-ramsey-number",
      "definition": "The diagonal Ramsey number R(n,n), which forces a clique or independent set of the same prescribed size n.",
      "prerequisite_concept_ids": [
        "r012:concept:ramsey-number"
      ],
      "source_label": "symmetric Ramsey number",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_ramsey_estimatesize",
        "r012:unit:s_ramsey_probability"
      ]
    },
    {
      "concept_id": "r012:concept:symmetric-relation",
      "definition": "A binary relation in which x being related to y always implies that y is related to x.",
      "prerequisite_concept_ids": [
        "r012:concept:binary-relation"
      ],
      "source_label": "symmetric relation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_exercises",
        "r012:unit:s_background_equivalence"
      ]
    },
    {
      "concept_id": "r012:concept:symmetry-aware-enumeration",
      "definition": "Counting equivalence classes of combinatorial structures after permitted symmetries are identified.",
      "prerequisite_concept_ids": [
        "r012:concept:equivalence-relation",
        "r012:concept:generating-function"
      ],
      "source_label": "symmetry-aware enumeration",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_polya"
      ]
    },
    {
      "concept_id": "r012:concept:symmetry-equivalence",
      "definition": "Equivalence of arrangements under an allowed symmetry such as rotation.",
      "prerequisite_concept_ids": [
        "r012:concept:necklace"
      ],
      "source_label": "same necklace under rotation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_enum",
        "r012:unit:fig_intro_necklace"
      ]
    },
    {
      "concept_id": "r012:concept:szemeredi-online-antichain-optimality",
      "definition": "The binomial upper bound for online antichain partitioning is attained by an adversarial Builder strategy.",
      "prerequisite_concept_ids": [
        "r012:concept:online-poset-antichain-partition"
      ],
      "source_label": "Szemerédi online antichain optimality",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_online"
      ]
    },
    {
      "concept_id": "r012:concept:technology-entrepreneurship",
      "definition": "Founding and operating a technology company with external investment.",
      "prerequisite_concept_ids": [],
      "source_label": "high-tech entrepreneurship",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:tenure-track-position",
      "definition": "An academic appointment on a formal path toward tenure.",
      "prerequisite_concept_ids": [
        "r012:concept:postdoctoral-position"
      ],
      "source_label": "tenure-track position",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:threshold-probability",
      "definition": "An edge-probability scale at which a random-graph property changes from unlikely to likely.",
      "prerequisite_concept_ids": [
        "r012:concept:random-graph",
        "r012:concept:with-high-probability"
      ],
      "source_label": "threshold probability",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_ramsey_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:tic-tac-toe-board-enumeration",
      "definition": "Counting 3-by-3 board states modulo the dihedral symmetries of the square.",
      "prerequisite_concept_ids": [
        "r012:concept:dihedral-group",
        "r012:concept:polya-enumeration-theorem"
      ],
      "source_label": "tic-tac-toe board enumeration",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:tile",
      "definition": "A prescribed shape used to cover a region without gaps or overlaps in a tiling problem.",
      "prerequisite_concept_ids": [
        "r012:concept:geometry"
      ],
      "source_label": "tile",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:a5fd615b1106d334b47d57d4"
      ]
    },
    {
      "concept_id": "r012:concept:topological-sort",
      "definition": "A linear extension of a finite partial order or directed acyclic dependency relation.",
      "prerequisite_concept_ids": [
        "r012:concept:linear-extension"
      ],
      "source_label": "topological sort",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_sorting"
      ]
    },
    {
      "concept_id": "r012:concept:total-order",
      "definition": "A partial order in which every pair of elements is comparable.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order",
        "r012:concept:poset-comparability"
      ],
      "source_label": "total order",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_posets_intro",
        "r012:unit:s_background_order"
      ]
    },
    {
      "concept_id": "r012:concept:tournament",
      "definition": "An orientation of a complete graph in which exactly one direction is selected for every pair of distinct vertices.",
      "prerequisite_concept_ids": [
        "r012:concept:complete-graph"
      ],
      "source_label": "tournament",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_ramsey_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:tower-of-hanoi-recurrence",
      "definition": "The recurrence for the minimum number of legal single-disc moves needed to transfer an n-disc tower between pegs.",
      "prerequisite_concept_ids": [
        "r012:concept:recurrence-relation"
      ],
      "source_label": "Tower of Hanoi recurrence",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:7ad32a20f169b1d58bcd7202"
      ]
    },
    {
      "concept_id": "r012:concept:transcendental-number",
      "definition": "A real number that is not algebraic.",
      "prerequisite_concept_ids": [
        "r012:concept:algebraic-number"
      ],
      "source_label": "transcendental number",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_complex"
      ]
    },
    {
      "concept_id": "r012:concept:transition-matrix",
      "definition": "The stochastic matrix of one-step state-transition probabilities.",
      "prerequisite_concept_ids": [
        "r012:concept:markov-chain"
      ],
      "source_label": "transition matrix",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_markov-chains"
      ]
    },
    {
      "concept_id": "r012:concept:transitive-relation",
      "definition": "A relation R is transitive when xRy and yRz imply xRz.",
      "prerequisite_concept_ids": [
        "r012:concept:binary-relation"
      ],
      "source_label": "transitive binary relation",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_order",
        "r012:unit:s_background_equivalence",
        "r012:unit:s_background_integers"
      ]
    },
    {
      "concept_id": "r012:concept:traveling-salesperson-tour",
      "definition": "A minimum-weight closed tour visiting every required vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:weighted-graph",
        "r012:concept:optimization"
      ],
      "source_label": "traveling salesperson tour",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_opt"
      ]
    },
    {
      "concept_id": "r012:concept:tree",
      "definition": "A connected acyclic graph.",
      "prerequisite_concept_ids": [
        "r012:concept:acyclic-graph",
        "r012:concept:graph-connectivity"
      ],
      "source_label": "tree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro",
        "r012:unit:prop_tree-leaves",
        "r012:unit:fig_spantree"
      ]
    },
    {
      "concept_id": "r012:concept:tree-child",
      "definition": "A vertex immediately below another vertex in the hierarchy induced by a tree root.",
      "prerequisite_concept_ids": [
        "r012:concept:rooted-tree",
        "r012:concept:vertex"
      ],
      "source_label": "child of a tree vertex",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots"
      ]
    },
    {
      "concept_id": "r012:concept:tree-root",
      "definition": "The designated vertex that supplies the orientation and parent-child hierarchy of a rooted tree.",
      "prerequisite_concept_ids": [
        "r012:concept:tree",
        "r012:concept:vertex"
      ],
      "source_label": "root of a tree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots"
      ]
    },
    {
      "concept_id": "r012:concept:triangle",
      "definition": "A clique on three vertices.",
      "prerequisite_concept_ids": [
        "r012:concept:clique"
      ],
      "source_label": "triangle",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_graph"
      ]
    },
    {
      "concept_id": "r012:concept:triangle-bad-event",
      "definition": "A chosen three-vertex set spans all three edges in the random graph.",
      "prerequisite_concept_ids": [
        "r012:concept:random-graph"
      ],
      "source_label": "triangle bad event",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_applying-local-lemma"
      ]
    },
    {
      "concept_id": "r012:concept:tuple",
      "definition": "A finite ordered list of objects.",
      "prerequisite_concept_ids": [
        "r012:concept:ordered-pair"
      ],
      "source_label": "tuple",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_products"
      ]
    },
    {
      "concept_id": "r012:concept:two-plus-two-poset",
      "definition": "The disjoint sum of two two-element chains.",
      "prerequisite_concept_ids": [
        "r012:concept:disjoint-poset-sum",
        "r012:concept:poset-chain"
      ],
      "source_label": "2+2 poset",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_fishburn"
      ]
    },
    {
      "concept_id": "r012:concept:uncountable-sample-space",
      "definition": "A sample space not enumerable by the natural numbers, requiring probability to be assigned to an admissible family of subsets rather than pointwise masses alone.",
      "prerequisite_concept_ids": [
        "r012:concept:sample-space"
      ],
      "source_label": "uncountable sample space",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_probability_infinite-outcomes"
      ]
    },
    {
      "concept_id": "r012:concept:union-axiom",
      "definition": "For every set of sets there exists a set containing exactly their elements.",
      "prerequisite_concept_ids": [
        "r012:concept:zfc-set-theory"
      ],
      "source_label": "axiom of union",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_ZFC"
      ]
    },
    {
      "concept_id": "r012:concept:unit-capacity-integral-flow",
      "definition": "In a unit-capacity network, an integral maximum flow assigns each edge flow zero or one.",
      "prerequisite_concept_ids": [
        "r012:concept:integer-maximum-flow-integrality"
      ],
      "source_label": "unit-capacity integral flow",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_flowapplications_intro"
      ]
    },
    {
      "concept_id": "r012:concept:universal-quantifier",
      "definition": "The logical quantifier asserting that every object in a domain satisfies a predicate.",
      "prerequisite_concept_ids": [
        "r012:concept:logical-quantifier"
      ],
      "source_label": "universal quantifier",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_notation"
      ]
    },
    {
      "concept_id": "r012:concept:unlabeled-graph",
      "definition": "A graph considered up to graph isomorphism rather than by particular vertex labels.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-isomorphism"
      ],
      "source_label": "unlabeled graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:unlabeled-graph-enumeration",
      "definition": "Counting graphs up to vertex relabeling through the induced pair-group action on possible edges.",
      "prerequisite_concept_ids": [
        "r012:concept:pair-group",
        "r012:concept:polya-enumeration-theorem"
      ],
      "source_label": "unlabeled graph enumeration",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_polya_apps"
      ]
    },
    {
      "concept_id": "r012:concept:unlabeled-poset",
      "definition": "A poset considered up to isomorphism rather than by particular element labels.",
      "prerequisite_concept_ids": [
        "r012:concept:poset-isomorphism"
      ],
      "source_label": "unlabeled poset",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:f_unlabeled"
      ]
    },
    {
      "concept_id": "r012:concept:unlabeled-tree",
      "definition": "A tree whose vertices are not distinguished by assigned names.",
      "prerequisite_concept_ids": [
        "r012:concept:tree"
      ],
      "source_label": "unlabeled tree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rubots"
      ]
    },
    {
      "concept_id": "r012:concept:up-set",
      "definition": "A set of elements lying strictly or weakly above a specified element or subset, according to the indicated notation.",
      "prerequisite_concept_ids": [
        "r012:concept:partial-order"
      ],
      "source_label": "up set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:para_posets_dilworth_proof"
      ]
    },
    {
      "concept_id": "r012:concept:upper-bound-constraint",
      "definition": "A restriction requiring an integer variable or allocated share not to exceed a specified value.",
      "prerequisite_concept_ids": [
        "r012:concept:distribution",
        "r012:concept:inclusion-exclusion"
      ],
      "source_label": "upper bound constraint",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:435387697278dbaa95cd68bd",
        "r012:unit:auto:328950a879727c218a6d3e20",
        "r012:unit:auto:1e317ac7ad56d3f690eee82d"
      ]
    },
    {
      "concept_id": "r012:concept:van-der-waerden-theorem",
      "definition": "For every number of colors and desired progression length, every sufficiently long initial interval of positive integers contains a monochromatic arithmetic progression of that length.",
      "prerequisite_concept_ids": [
        "r012:concept:arithmetic-progression",
        "r012:concept:ramsey-property",
        "r012:concept:positive-integer"
      ],
      "source_label": "finite-color arithmetic-progression theorem",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:2c43873e0968cfc6d26f9acb"
      ]
    },
    {
      "concept_id": "r012:concept:variance",
      "definition": "The expected squared deviation E((X-E(X))^2).",
      "prerequisite_concept_ids": [
        "r012:concept:random-variable",
        "r012:concept:expected-value"
      ],
      "source_label": "variance",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:dd704af3675a6c3b2f7eb811"
      ]
    },
    {
      "concept_id": "r012:concept:vector-space-basis-and-dimension",
      "definition": "A basis is a linearly independent spanning family; its cardinality is the dimension, and every vector is a linear combination of basis vectors.",
      "prerequisite_concept_ids": [
        "r012:concept:real-vector-space",
        "r012:concept:vector-subspace"
      ],
      "source_label": "basis and dimension",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_rigorous_principal",
        "r012:unit:thm_advance"
      ]
    },
    {
      "concept_id": "r012:concept:vector-subspace",
      "definition": "A subset of a vector space that is itself a vector space under the inherited operations.",
      "prerequisite_concept_ids": [
        "r012:concept:real-vector-space"
      ],
      "source_label": "subspace",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_advance",
        "r012:unit:lem_particular"
      ]
    },
    {
      "concept_id": "r012:concept:venn-diagram",
      "definition": "A diagram whose regions represent sets and whose overlapping regions represent set intersections.",
      "prerequisite_concept_ids": [
        "r012:concept:set-membership"
      ],
      "source_label": "Venn diagram",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:exa_inclusion-exclusion_students",
        "r012:unit:fig_venn-app-comb"
      ]
    },
    {
      "concept_id": "r012:concept:venture-capital",
      "definition": "Investment capital supplied to a high-growth enterprise.",
      "prerequisite_concept_ids": [
        "r012:concept:technology-entrepreneurship"
      ],
      "source_label": "venture capital",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:ch_epilogue"
      ]
    },
    {
      "concept_id": "r012:concept:vertex",
      "definition": "An element of the vertex set of a graph.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "vertex",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_graph",
        "r012:unit:fig_graphdata",
        "r012:unit:fig_connectedgraph",
        "r012:unit:s_networkflow_intro",
        "r012:unit:s_networkflow_flows-cuts",
        "r012:unit:s_networkflow_augmenting",
        "r012:unit:alg_labeling",
        "r012:unit:s_networkflow_example",
        "r012:unit:s_networkflow_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:vertex-degree",
      "definition": "The number of edges incident with a vertex, equivalently the size of its neighborhood in a simple graph.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-incidence",
        "r012:concept:vertex-neighborhood"
      ],
      "source_label": "degree",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro",
        "r012:unit:thm-graphs-first",
        "r012:unit:rq-graphs_intro_degree"
      ]
    },
    {
      "concept_id": "r012:concept:vertex-neighborhood",
      "definition": "The set of all vertices adjacent to a given vertex.",
      "prerequisite_concept_ids": [
        "r012:concept:graph-neighbor"
      ],
      "source_label": "neighborhood",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphs_intro",
        "r012:unit:fig_small_graph"
      ]
    },
    {
      "concept_id": "r012:concept:vertex-potential",
      "definition": "The third label coordinate, equal to the maximum update amount known along the recovered augmenting path prefix.",
      "prerequisite_concept_ids": [
        "r012:concept:ford-fulkerson-labeling-algorithm"
      ],
      "source_label": "potential of a labeled vertex",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:alg_labeling"
      ]
    },
    {
      "concept_id": "r012:concept:vertex-set",
      "definition": "The set of vertices of a graph.",
      "prerequisite_concept_ids": [
        "r012:concept:vertex"
      ],
      "source_label": "vertex set",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:auto:6691548129df37fcc64c5423"
      ]
    },
    {
      "concept_id": "r012:concept:weighted-digraph",
      "definition": "A digraph paired with a nonnegative weight or length on every directed edge.",
      "prerequisite_concept_ids": [
        "r012:concept:digraph"
      ],
      "source_label": "weighted digraph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_graphalgorithms_shortest-paths"
      ]
    },
    {
      "concept_id": "r012:concept:weighted-graph",
      "definition": "A graph whose edges or vertices carry numerical weights.",
      "prerequisite_concept_ids": [
        "r012:concept:graph"
      ],
      "source_label": "weighted graph",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_intro_opt",
        "r012:unit:fig_wgraph-1",
        "r012:unit:fig_spantree-1",
        "r012:unit:s_graphalgorithms_min-wt-span"
      ]
    },
    {
      "concept_id": "r012:concept:well-defined-operation",
      "definition": "An operation whose result is independent of the representatives selected for its input classes.",
      "prerequisite_concept_ids": [
        "r012:concept:equivalence-class",
        "r012:concept:binary-operation"
      ],
      "source_label": "well-defined operation on equivalence classes",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_prop-integers"
      ]
    },
    {
      "concept_id": "r012:concept:well-ordering-principle",
      "definition": "Every nonempty set of positive integers has a least element.",
      "prerequisite_concept_ids": [
        "r012:concept:positive-integer"
      ],
      "source_label": "Well Ordered Property of the Positive Integers",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_induction_posintsord",
        "r012:unit:princ_well-order"
      ]
    },
    {
      "concept_id": "r012:concept:with-high-probability",
      "definition": "An event whose probability tends to one as the size parameter tends to infinity.",
      "prerequisite_concept_ids": [
        "r012:concept:probability-space"
      ],
      "source_label": "with high probability",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:thm_girth",
        "r012:unit:s_ramsey_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:zero-flow",
      "definition": "The feasible flow assigning zero to every directed edge.",
      "prerequisite_concept_ids": [
        "r012:concept:network-flow"
      ],
      "source_label": "zero flow",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_networkflow_intro",
        "r012:unit:s_networkflow_exercises"
      ]
    },
    {
      "concept_id": "r012:concept:zero-one-matrix",
      "definition": "A matrix all of whose entries are zero or one.",
      "prerequisite_concept_ids": [],
      "source_label": "zero-one matrix",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_kitchensink_zero-one-matrices"
      ]
    },
    {
      "concept_id": "r012:concept:zero-root-shift-reduction",
      "definition": "If p(A)=A^m q(A) with q having nonzero constant term, solutions of p(A)f=g correspond by an m-step translation to solutions of q(A)f=g.",
      "prerequisite_concept_ids": [
        "r012:concept:advancement-operator-polynomial"
      ],
      "source_label": "zero-root shift reduction",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_recurrence_adv-ops_zero"
      ]
    },
    {
      "concept_id": "r012:concept:zfc-set-theory",
      "definition": "Zermelo–Fraenkel set theory together with the axiom of choice.",
      "prerequisite_concept_ids": [
        "r012:concept:set-theoretic-foundations"
      ],
      "source_label": "ZFC set theory",
      "status": "source_frozen",
      "unit_ids": [
        "r012:unit:s_background_ZFC"
      ]
    }
  ],
  "course_id": "C70",
  "schema": "c70-concept-index/1"
}
